I think there Rollbots and other casino perks is what makes them rewarding and not the RTP for each game because it was set by the provider and not the casino.
This is what a lot of people think but it's just not true.
For instance Sweet Bonanza:
Roobet: 95.5% RTP
Stake 96.6% RTP
Rollbit 96.6% RTP (effective RTP with rewards 98.6%)
So at least Roobet has lowered their RTP from what Pragmatic normally is.
I didn't know that casinos can change their RTP on the same game as others up until now.
OP I think if you play enough on a single casino you get more benefits and rewards so that may be case to case per person. I don't think that we can rank casinos to which one is the most rewarding. I often play in different platforms but I always come back to the ones with weekly rewards.