This is a great response, and you cover a lot of the mechanics on the "plumbing" that don't get enough press coverage. It doesn't help the RH CEO is unable to articulate it in an interview, which makes him seem shady by default.
I'll add one point. The daily volatility in the stocks like GME is truly unprecedented. In a crisis, everything goes down. In this case, you have random stocks moving 50-100%/day, and they are dominating market volume. For example, one day GME was the #1 traded stock in the market.
That is why DTCC raises this requirements. And a smaller clearing broker like RH will have some stress posting collateral. Other brokers had this problem too. For those saying this never happened before, it is true but there is a reason
The more I read, I think it is possible there was some shadiness (because of the connections among players), but more probable it was related to the extreme volatility
As another posted pointed out, Citidel makes most of their money as a market maker. When stocks prices jump around like that, it actually makes it more difficult for them to make money
I would encourage everyone to read articles from Matt Levine from Bloomberg. It is free to get on his mailing list. And he explains many of these topics in a clear way, without an agenda. And he does call people out for shady behavior when it happens