Changes to The Boys
First, don't take away Season 5's budget for Vought Rising.
I'd keep Seasons 1-3 the same. From Season 4 - The Trump parodies can stay, but mainly in theme. You can parody Trump without making Homelander an idiot and not his own character (Like Daredevil did with Kingpin). I'd make sure to keep Homelander his own character and flesh him out more. In general, keep Homelander scary, competent and disturbing as he was in Season 1 and Season 3. Yes, he is supposed to have a mental breakdown, and him losing it is kind of the point, but making him lose it and revealing his pathetic self doesn't mean you need to make him a caricature with no feats.
No Sister Sage. Taking over the presidency is fully Homelander's plan. Cut out the Colin and Frenchie useless plotline. More Joe Kessler and a better setup for Butcher's arc. I actually liked what they did with Hughie and his father. More MM. They had the right direction when they focused on his vendetta against Vought in Season 3, but they kind of sidelined him for Kimiko and Frenchie. MM becoming more cynical in Season 5 doesn't feel earned. Use The Legend as a plot device for world-building.
The POV Episode in Season 5 of Firecracker and Noir 2 should be moved to Season 4.
Season 5 should feel actually schorched Earth. First, cut out all of the Vought Rising setup. Break the status quo: More time of The Boys in the freedom camps. Butcher should betray The Boys much earlier and go solo, but there should be some reunion, so he actually manipulates them and lies about the virus. It was very odd that Annie and Kimiko just agreed to use the virus and there was no conflict about it. It should have been the center of the conflict. Butcher is lying to them while he is planning on actually killing them both.
Ryan should join The Boys and build a connection with MM, if we keep MM eventually raising him. I don't think Soldier Boy is necessary, but he's a fan favorite, so we can find a place for him.
I will keep Homelander's God arc, but make it actually disturbing and creepy and a new level for his psychopathy, like his final speech in Episode 8. The Flight 37 video is leaked in Episode 6 during a press conference, where Homelander is giving the speech of "I shall remain eternal, God of the Ashes" (I'll replace God of the Ashes with "King of Hell", a reference to his line from the comics), Homelander recklessly kills all the journalists there in front of the whole world, a full, brutal massacre that should be hard to watch and and include a YouTube viewing warning.
The last half of Episode 6 and all of Episode 7 focus on Homelander's rampage and becoming "God of the Ashes" and "King of Hell". Basically, a longer, more gory version of Tighten's rampage in Megamind. Homelander kills The President in the final of Episode 6. Homelander loses all of his supporters aside from a devoted cult and some Billionaires that seek to profit from the destruction he is causing. Homelander decides to kill off the non-believers. I'd also give him a power buff. Ashley betrays Homelander and tries to stage a coup against him, but he kills her on the place and this is where her story ends.
I feel like Butcher should also go on a rampage against Supes who work for Homelander to establish his threat, also.
In Episode 7, Butcher and The Boys are forced to work together as Homelander is doing everything he said he would do in Season 3, but they don't trust him. The final fight between Butcher and Homelander is a longer, more climactic version of the Herogasm fight. If we keep Soldier Boy then this can be the point where he depowers both. Homelander's death feels more disturbing, with flashbacks to his childhood.
Episode 8 focuses on The Boys attempting to stop Butcher and the epilogue of the fall of Homelander, and dealing with the consequences for his massacre. New York should be in ruins.
Another thing I would do is put more focus on how regular people see superheroes and focus from the regular people's perspective, like they did a lot in seasons 1 and 2