Correct me if I'm wrong, but is that what the "Rainbow Rocket" thing is? To have all the older team leaders join together under the name "Rocket" is blatant gen 1 pandering because honestly, a lot of the villains' personalities circles around their pride of being the center of their own teams. Characters like Lysandre and Ghetsis--I would never imagine them abandoning their team name for the sake of joining with other villains.
Then there's the issue of worldbuilding consistency. SM/USUM clearly take place after all the other main series games because Grimsley's concept art is titled "two years after [B2W2]." So for the all the older villainous team leaders to appear, what does that imply? Okay, they can throw all theories of Lysandre dying out the window (but poor Sycamore, guess the player defeating Lysandre didn't "save" him after all!) to make him appear here; same with Giovanni. Alright, sure, Platinum doesn't exist, Cyrus isn't trapped in the Distortion World, that's fine. The Shadow Triad said Ghetsis is completely incapacitated? Uhh.... they lied! Yeah! He's totally fine and absolutely willing to join other villains despite being the most hubris-inflated villain in the series!
Maxie and Archie... repented? And... gave up their ways of being a villain? Oh uh... w-we can ignore that...!
What? We actually followed Colress's lore and had him appear in SM as a good guy already? So Maxie and Archie appearing as villains can't be justified at all?! Oh shoot...
Yeah, this idea of "Rainbow Rocket" just screams "bad fanfiction" to me. I know that the narrative of the main games hasn't been as good since gen 5, but still, they've worked hard on their lore and world-building, to the point where they basically turned the series into a "Zelda timeline" for the sake of not letting ORAS completely retcon RSE. This would destroy literally years worth of world-building, and for what?
I'd rather Team Rocket be working alone and see characters like reformed Maxie and Archie in the Battle Tree.