Assuming, there's a certain game system that is very effective in giving profits that the rest don't you think that's the only game gamblers will be gambling with because we are all looking for profits whether, gambling for fun or not. There's no game that is more profitable than the other because luck is what brings your profit and not the game itself.
I think that before settling on one particular game, a player will usually try their hand at a bit of everything a little roulette, some slots, some betting. In the end, everyone chooses the game, that in their opinion suits them best. But I agree that in most of these games, luck plays the decisive role. Even those players who believe that in betting they have much more control than for example in slots, are still heavily dependent on luck.