Unfortunately, this is not 100% correct information. RTP can be adjusted and that is why different casinos have 1-2% difference for same slots by same provider, casino can decide which option is best for its own advantage. Negative thoughts is caused by house edge which is unbeatable in the long term, as explained before players can't beat the casino but player can.
Not entirely sure but when a casino is using a game provider then RTP and such things are not in casinos control. The provider adjust it depending on the game. The casino is only responsible to bring clients in their platform and let the clients to play. Bet history and everything else except customer management are done by the provider.
These days unless you are a big casino, you can not afford your own system. You are just using others API. I guess bet365 are big enough to have their own game engine and sports engine. I could be wrong.
AFAIK, casinos have control of RTP. For example, Dog House Megaways slot by Pragmatic provider has a 3.57% house edge on Stake according to a description page of Stake slot info.
Slotcatalog explains it this way : "The Dog House Megaways slot Pragmatic Play has RTP ranges. RTP ranges is a game feature when Casinos have the possibility to adjust RTP according to their needs. The RTP ranges could be quite wide. For some games, it varies from 80% to 97%. Pay attention. RTP less than 92% is not applicable to the casinos with the MGA license." Checked other casinos and same slot has different RTP range, so I am not also 100% sure how they adjust, we only have general information.