Only someone who doesn't understand how any of this works would believe these absurd conspiracy theories.
1) Citadel is one of FIVE of wholesale market markets RH use. Even if they did refuse to accept orders for GME, why wouldn't their four main competitors not happily accept them if it meant blowing up the biggest player in the field? They have no incentive to help Citadel. In fact, they have a clear financial incentive to do the opposite.
2) Why would RH care if Citadel went away? Citadel is one of their five 'suppliers' if you will. If Citadel disappeared overnight, RH would just route their order to the others. It makes absolutely no difference to them. They just route to whoever currently pays the most for orderflow.
3) RH customers are extremely small players with next to no capital between them. Cutting them off makes no difference, because it was professionals with real money driving the squeeze at that point. They recognised that they could make a ton of money, and put a bunch of competitors out of business in the process, so they kept hammering the stock.
4) The claim that Citadel itself even had a GME short position (beyond their MM inventory) is baseless. Citadel Advisor's previous 13F filing shows that they were outright LONG GME stock, were LONG GME calls, and were LONG GME puts. So while those puts will have lost money, the other two positions will have GAINED MASSIVELY during the squeeze. Their short exposure was mainly via the money that they lent to Melvin Cap during the squeeze.