THE "WEIRD ROUTE" IS A REVENGE PLOT: A potential crack theory that just might make sense
To start this off strongly and clearly, I have a bizarre but possibly plausible theory that the "weird route" is actually all a meta revenge plot by the soul against both the Holiday family and Kris. Just keep in mind that I'm basing this off of the popular idea that Dess is the Knight and Carol knows about the soul—they are all working together, aware of the soul and using it for something.
To start, let's look at the actions and potential metaphors in the Snowgrave Route in chapter 2. A main thing in this route is pressure and a "snowglobe", which we see Noelle within much like how we, the soul, are within a "cage" (Kris). This somewhat establishes a deliberate parallel in which someone is being trapped and controlled just like us. Chapter 2 is all about beginning to establish our cruel control over Noelle, IN PARTICULAR, MIND YOU. Note how there are no options to pressure or even react to others in this path like Susie, Ralsei, Berdly, Toriel, etc... We specifically choose Noelle for this.
Next, in Chapter 3, things proceed as normal and seemingly face no change until...The Knight appears. I was just watching a blind playthrough of the "weird route" and someone's attempt at beating The Roaring Knight for the first time in the same playthrough, and something I noticed is subtly increased aggression. Attacks appear only slightly faster but there is a notably brand new move that was either added post-release for no real reason or exclusive to the weird route. What is this attack? It's when The Knight fires a flurry of diamonds from their fingertip before said diamonds stall and burst into additional bullets. HOWEVER, in the weird route, there exists a harsher variation of this move. When the diamonds burst, the resulting bullets are red and home in on you before moving. If the "Dess is the Knight" theories hold water...that means Dess may have an idea of what we've done to her sister in the previous chapter and is showing more aggression than usual because of it. It's not just a "weird route" exclusive challenge. It's a small hint that she has a bad feeling about us, the soul, and is beginning to see a genuine threat. It's now personal. Of course, you're expected to fight back as much as possible in this path. Hence, the additional attack...
Next, in Chapter 4, I think this is where the biggest red flags show. I think that, during the section of visiting the Holiday residence, the original intent during a normal route is to look for a code and investigate the mystery. In the "weird route", however, you ignore this objective entirely. **Your target is Noelle**. You don't care about the code. You don't care about the mystery of the bunker. YOU KNOW what's happening and are now going after someone uninvolved, yet ultimately, intimately related to those who are. You ignored your objective purely to torment Kris and further corrupt Noelle, in particular. There's an obvious conspiracy going on between Carol, The Knight and Kris involving the soul, as the soul is confirmed to be required by Kris to enter the Dark World and seal fountains. This potentially establishes the idea that the soul is being used. It is not a convenient plot device. It was intentionally taken control of by force and is the impetus of a plot by half of the Holiday family and Kris. It's a motive for our increasingly violent and manipulative rebellion. This is no longer about uncovering the mystery. **This is about insidiously destroying Kris and getting revenge against half of the Holiday family through Noelle**. It's also why there's a clear, antagonistic disconnect between Kris and the soul, I.E. the legendary bathroom crashout scene. We're forcing Kris to do something deplorable and against both their will and script, and they hate it on a personal level. They HATE us, but they NEED us.
Finally, there's chapter 5. The beginning speaks for itself. Kris is laying in bed, dead silent and implied to have been there all day. Kris is broken and mortified. The fact you have to forcefully drag them out of bed while there is clear resistance...I think suggests an almost pathetic, silent plea. "Please, no more. Please, stop. Don't make me do anything else." We're establishing a violent rebellion here, fighting Kris for their own autonomy and body. We're fighting to control the plot that Kris and their co-conspirators are losing control of. They thought to use and control us, but "SINCE WHEN WERE YOU THE ONE IN CONTROL?" Is effectively our response. We effectively skip the ENTIRE DARK WORLD of this chapter, further nailing in the idea that our objective is not to solve a mystery but to break a script. The soul broke Noelle and is being made to join her in crossing the river through sheer will and persistence. Through...determination, you could even say.
Undertale references aside, the story here is notably shorter and almost hollow here, as if the soul is hyper-fixated on something we, the player, were not informed of. There is a particularly strange fixation on harsh control, obsession with Noelle in particular, and a total diversion from the intended script that could all just be a distraction. I think there are some implications that this isn't just us trying to break the script for no real reason. This is a meta revenge plot by the soul that we, as the players, just aren't aware of yet. We're using Noelle, specifically, to hurt everyone involved as much as possible. This is a declaration of war against the ones using us, and as the saying goes...in love and war...
Conclusion/TL;DR: The "weird route" isn't senseless. It's deliberate. It's us breaking the script out of rancor and denying our fate as a tool, but we're disregarding the costs and moral implications. We, the player, just don't realize it yet. Like before, we are not ENTIRELY the soul. We just influence it heavily, and we are expected to meta-game or have "impossible" knowledge.