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.