As an example let’s look at Rise of Merlin slots which already has poor RTP: https://i.imgur.com/WwAZhgj.png
And reality from hundreds of thousands of spins: https://i.imgur.com/Znbg1WS.png
So casino can offer you gazillion of bonus dollars with low wagering, but they are in Donald Duck country with illusory regulation and they can tweak RTP as they want.
