To maintain some Semblance (ha) of balance, this super mode would not only drain a massive chunk of Aura, it can also only be achieved when a Huntsman acts in perfect alignment with their core philosophy that they bury deep inside. Once the mode ends, the user's Aura is completely exorcised, which leaves them physically exhausted and vulnerable.

Ruby for me, especially with the drama it would bring between Qrow and the group.

I'm talking the Belladonnas, Ilia, and the new Fang alliance under Ghira's new leadership.

Grimmification refers to the transformation or fusion of a living human/Faunus with the Grimm.

Considering how… controversial she is as a major sour point in the series, especially during Volumes 1 and 5.

Overall, I think the three main things that needed to be done are:

Tsumiki Fushiguro

Tsumiki as a character needed to actively show us why she's Megumi's moral anchor. Giving her more of visible presence in the early arcs would've given Megumi’s arc more weight.

Tsumiki should've started out as more of an active character in the early arcs. Whether that be through packing bento boxes for him or scolding bout his injuries, just anything to establish contrast between Megumi’s Jujutsu world and the mundane world he wants to protect. While we're at it give Tsumiki on-screen interactions between Yuji and Nobara, which could maybe have her embarrass Megumi by treating him like a kid.

This could also give credence to Megumi's philosophy on heroism, which is a classic case of telling us this philosophy, but not truly showing the foundations. Have their be flashbacks detailing how they handled Toji's abandonment. The philosophy foundations could best be shown in an argument between the two, highlighting the contrast between Megumi's cynicism and Tsumiki's idealism. Have Megumi grapple between the two halves constantly.

When Tsumiki finally awakens for the Culling Games, having her be immediatly possession by Yorozu ruined any chance for her to be seen as anything more then a prop. Have her actually wake up as herself first for a poignant reunion where she can actively see how much he has grown and express horror at the dangerous world he entered to save her from. When Yorozu tries to take over, Tsumiki’s soul should actively fighting back from within in the same vein as Yuji and Sukuna.

Ten Shadows Technique

His taming over the Ten Shadows technique should've been more about actively unitilizing the shadows and focusing on fully completing Shadow Chimera Garden, rather than just being the precursors to MAHORAGA.

Megumi needed to conquer every untamed Shikigami, complete his DE, and merge each shikigami ability over the course of every arc he's in to give him a sense of earned progression instead of giving all that to Sukuna. Dedicate mini-arcs or extra battles during the Culling Game where Megumi tames Piercing Ox, Tiger Funeral, or Round Deer.

While we're on shikigami, expand on his ability to fuse them together so that we could get more creative combinations. Like imagine him combining Nue and Great Serpent into a massive, flying electric leviathan, or merging Max Elephant with Piercing Ox to create a crushing stampede of high-pressure water.

Finally, he should've completed his DE before the Shinjuku Showdown so that he could trap enemies in his ocean of shadow, which would include completely cutting off their footing. Imagine Megumi seamlessly morph his own body into his own domain, creating perfect shadow clones of himself, and manifesting any combination of Shikigami instantly from every single angle.

The narrative bottleneck of Megumi’s character was "With this Sacred Treasure" as the ultimate IHYLD move. Instead of Mahoraga, Megumi needed to sacrifice narratively potent Shikigami so that the power could merge into his remaining beasts (or preferably himself) to construct a Mahoraga-like entity under his control. Or, if that isn't good, show Megumi duking it out against Mahoraga alongside Yuji in a desperate bid to actually tame it.

Shinjuku Showdown

Megumi needed to be more of a saboteur fighting Sukuna from the inside out, culminating in an internal rebellion that directly enabled Sukuna's defeat.

When Yuji entered Sukuna’s soul footprint to reach Megumi, he shouldn't be so immobile and useless during the final battle, even if it was "realistic". He needed to be actively fighting whenver Sukuna goes all out so that his output fluctuates. This could even go all the way back to the Gojo v. Sukuna fight, with Megumi using his own DE from within the shadow of Sukuna’s soul and destabilizing the barrier from the inside, giving Gojo a tactical opening.

Even though Sukuna tamed and destroyed many of the Ten Shadows, the core rule of the technique is Inheritance. As Sukuna’s physical body weakened from Yuji's raw hands, Megumi could sever Sukuna's access to the remaining Ten Shadows, channeling the power of the destroyed Shikigami directly into his own soul to protect his mind from Unlimited Void.

The climax should've been a coordinated strike between Yuji and Megumi against Sukuna. In the final moments of the fight, as Yuji prepares his ultimate Black Flash, Sukuna's own shadow could rise up and chain his feet to the ground, preventing him from dodging. This could give Megumi the ultimate hand in his own rescue and Sukuna's defeat.

Let’s be real, however tragic may it be, Winter Schnee's death would probably the most satisfying way to wrap up the Schnee side story, as it makes total sense in terms of Weiss’s character development.

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First off, her name. Monty’s color-naming rule means that characters are walking manifestations of their design and role. Winter Schnee is a name that simply describes the season. Weiss however, means white, which is more or less the colorful essence of the season. By naming the older sister Winter, CRWBY created a character whose entire identity is tied to a mantle she was always meant to pass on. Weiss's name implies she would be the ultimate destination for that winter motif. To add onto the death flags, Maiden magic transfers based on the dying Maiden's last thought. Which means that the transition between Maiden wielders is based on the connection one has for another. Winter’s entire character arc has been a journey from a cold obeyer of Ironwood's orders into a warrior for the common people and those that she absolutely cares about. She broke away from Ironwood's sinking ship specifically because of her love for Weiss. They spent multiple volumes building up Winter into a more and more protective sibling, so if Winter is mortally wounded, her final thought would most likely be Weiss. And even then, we already know Cinder is obsessed with stealing all the Maiden powers, and they alresdy fought before in Volume 8, so there's also the vendetta added onto that as well. Winter fights Cinder to protect the Atlas refugees. If Winter wins for a second time, Cinder could never, EVER recover in terms of threat factor. She has to win if they ever duel so that Cinder's crusade actually has more of a success rate. The only narrative way out of that corner is for Winter to hold Cinder off, take a fatal blow, and use her final breath to deliberately think of Weiss. This uses the magic rules to pull the power right out of Cinder's grasp at the last second, passing it to Weiss and giving Team RWBY a fighting chance.

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Secondly, having Weiss inherit the Winter Maiden powers will add onto her development as a Huntress and make her stand out even more from her family members. Winter had always stood like a pillar of support to Weiss, considering that Winter has been protecting her from most of the dangers in her life when she was around, sans the Fall of Beacon. As a result, being one of the main four lead characters, Weiss will have to break those harnesses by not having a sister anymore to come to her aid in case she fails. Weiss could prove that she is capable of protecting not just a couple of people, but the remaning vestiges of all of Remnant. The whole reason of being a protagonist in early volumes had been that Weiss was trying to make herself independent from her family legacy both financially and by name, but it'd be an interesting subversion if instead Weiss would need to revive the Schnee legacy, as she herself would be the symbolic heir to Atlas. Yet we also can’t forget about the mental impact when the transger, since the Maiden powers might as well be a constant blaring reminder of her sister’s sacrifice. Whenever Weiss uses them, she would probably be thinking about how Winter sacrificed herself for her younger sister. It will put an enormous weight on her shoulders and test her limits.

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Finally, the Schnee name has been fully stained by the shadow of exploitation and abuse that spread itself amongst the SDC. So if Weiss gains access to the Winter Maiden powers, the legacy of her family may actually take on a course that will not necessarily be linked with such corrupt practices. Since the citizens of Vacuo hate both Atlas and the SDC, due to the company extracting natural resources out of the desert for decades, the refugees from Atlas are coming into a kingdom that dislikes them from the get-go. Weiss might use her powers for humanitarian purposes and help citizens in some way, like giving water to those citizens that need it, or creating barriers to protect from Grimm. And finally, let's consider Willow and Whitley. They have been branded as part of the corrupt and rich family all this time. If one of them is proven to be protecting hundreds, their status can be changed to being part of the coalition. This would be especially useful when it comes to Whitley, as he already showed himself to be a child prodigy in terms of logistics and coordination, so he could help Weiss in the relief efforts so that she has space to fortify the city. All of this can allow some sort of compensation and build a new legacy from her late father's sins.

I mean, since her Silver Eyes is one of THE main tools in stopping Salem and the Grimm, why didn't Ozpin even so much as tell her about it at all before the Fall? He never so much as taught her personally on how to use them for a WHOLE YEAR?

And isn't Qrow ine of Ruby's teacher back at Signal? Qrow works for Ozpin, so why did he never tell Ozpin about Ruby having Silver Eyes until he saw her at the start of Volume I? And even so, him not even giving a hint as to her true potential feels like such a massive oversight for a seemingly wise chessmaster.