Both of you, please cool it.
I am cool?
Regarding stations of canon, I think a lot of people misunderstand what that actually means.
Stations of canon is the Wave Mission in Naruto always happening regardless of how the worlds been changed before-hand, (Like Kiri not being as fucked up) or still happening despite Naruto's team being different, their temperament being different, hell the temperament and attitudes of other teams and so on. So much had to align for Team 7 to get that mission that is basically unfeasible that it could happen a second time with even a minor tweak, or that it'd go exactly the same if the team make-up was different or Naruto were a different person, ETC.
RWBY's Fall of Beacon of Cinder's Atlas Arc ambush are not stations of canon by any means.
Cinder's plan during the Vale Arc was not heavily disrupted because no one among RWBY knew or had reason to suspect she existed, while the adults only knew "Queen Had Pawns" which could be Roman & Adam, or could be a middle management type as Cinder was, but that's all they know. Otherwise her plan hinged on only a few things, the Breach was genuinely sabotaged; she was able to roll with it but it still did way less damage than if it had been triggered later, let alone if the plan was to coincide it with the main attack on Beacon, if that had happened Vale would have fallen no doubts.
Meanwhile in V8, the heroes have zero reason to think Neo survived Monstra's explosion, zero reason to think Cinder has the password, zero to minimal reason to think Cinder had the intel, resources or allies to interrupt their plan. & what little they do have to suspect they can't plan on because they are on a time crunch with very little freedom of movement given the circumstances.
If one wanted to use a crossover character to disrupt say, the Fall of Beacon there's two ways to do it:
1: Happenstance leads them to have suspicions about Cinder's team.
Such as seeing Emerald & Mercury leaving Tuckson's book trade and then finding the man dead. This could literally unravel the entire god damn plot on Cinder's end, if Leo is contacts, her files accessed, and so on. But this could also happen in universe thanks to Yang wanting to buy Blake a nice present, its pure happenstance.
2: The cross over over character has some form of skill or power that is helpful in a way the cast did not originally have access too:
Such as say Cassandra Cain being a detective who can read body language so intimately she can predict people's actions. She'd likely pick up on 'something' being off with Cinder & co, and have skills and experience analyzing and tracing things down, as well as existing outside the context of Remnant and thus not having (For example) biases against Faunus to figure something out.
Or having a shape shifter who can infiltrate and spy on the White Fang, or someone with passive mind reading being like, "Damn, why is that gothic lolita always thinking about murder & that smarmy redheaded criminal? Someone should look into that!"
Conclusion:
You'll notice neither of these are disruptions that would come about because someone is tasty in a fight. Because being good at fighting is the one thing the RWBY cast has consistently had in excess, so unless the person is so powerful they can stomp the setting, they cannot actually disrupt Cinder & Co's plan without happenstance.
Maybe the Breach would be less damaging if someone from Symphogear was on hand to forcibly stop the train from ever hitting its mark. Maybe Pyrrha survives because Nightcrawler can teleport in and take her somewhere safe before Cinder shoots her through the heart.
But as far as stopping the plan from reaching at the very least the phase were its triggered? Being good in a fight is by itself, not going to do a thing. Hell, Cinder's plan didn't even rely on using the heroes. If RWBY lost to FNKI she could just have Flynt or Neon be tricked into attacking someone and use Vale's justifiable concerns about Atlas to rile people up. The plan is hard to disrupt because unless someone already knows Cinder is a threat or Emeralds Semblance, there is no way to really preempt it.
Hell, we saw Ruby get so very close in V3 and was just barely kept busy long enough for things to stay on the rails, and if Ironwood hadn't been able to make it down to the Vault in time in V8, Winter would have joined the battle against Cinder and likely been enough to turn the tables. But those potential disruptions were only possible once people had enough information to act on, or the freedom to act, which is not a given.
So yeah, that's my stance on that XD
Sorry for not having much to offer on the Sentai idea, I have little knowledge of the series and so can't say much.