It’s the people who put more time and money into them that will win them more often overall.
I really don’t like the call to make these things fair for all because, where does it stop?
Limit the amount of money allowed to invest? Post your biggest win won during the bonus round - you are allowed a max of 5 bonus round?
the promotion is to get people playing the game, if someone invests a load of money into it trying to win it, well, that’s the idea, for the casino to have more traffic on the game then it would have otherwise had. The promotion isn’t about fair treatment, it’s about promoting a game and increasing revenue from said game. Putting limits on the way in which that revenue can be gained, ie, removing bonus buys, will only reduce revenue. Would be an anti promotion.