What is clear is that cryptocurrency casinos are taking market share away from fiat casinos, as if the former did not exist, business would shift to the latter. However, I think that what the OP is suggesting is unlikely if we are talking about a big transfer, as there are people who only bet in fiat casinos, have never used cryptocurrencies and have a great distrust of them, and these people are not going to switch to crypto casinos, especially not overnight.
I don't think so.
At the time when the Covid-19 pandemic had started, casinos in general had a significant increase in users.
I'm sure that crypto casinos grew the most and I even believe that initially they may have "stolen" users from fiat casinos.
However, with the rise in popularity of casinos in general, many people who had never played at an online casino before began to participate, both crypto and fiat.
I believe both casinos have benefited from this popularity and surge in user traffic at online casinos.
Yes, the point is that with COVID there was a huge increase in online business, and both fiat and crypto casinos benefited from it, so I don't think the OP is right in what he says.