Did musk explicitly claim he expected exceptional returns? I don't think I'd be surprised either way, but I'm not sure what he's actually said.
As for timing there's no universal answer, stock changes are usually announced a few trading days before it's effective so funds can use that time to perform their rebalances. I presume most of the funds that needed to start tracking SPCX started buying pretty early so they were properly balanced on the day it took effect it might have even been part of the initial pop though they could have also waited for the first tranches of insider shares that were released (I think there were some relatively early releases as part of the IPO?).
They managed to maneuver "immediately and with no profit" and now they're tanking. That's bad, all of us with a 401k are losing money because of it. The people pointing this out are not the problem, SpaceX's (or I should say xAI's performance) is the problem.
I understand that investments made during the short lived peak would have lost money and that some amount of 401k will have lost money, but only for the purchases of indexes made during the peak, that may be substantial however, I'm not sure how transitions that add or remove stocks from an index work, there must be some mechanism to soften the impacts of the change, but I'm not an expert in that field.
Is it your contention that if they had have followed the standard path for inclusion, and then went on to have a similar share performance, then you would be OK with it?