Even as a criminal, the main story doesn't let a lot of the protagonists do too much of horrid things aside from Trevor.
To play Devil's Advocate with GTA 5 (and this is coming from someone who has a list of issues with that game but I gotta also be fair), it wouldnt be in character for Micheal and Franklin to do the more horrid missions. What they do in the open world is (usually) non canon actions by the player, that is until a cutscene starts playing.
Micheal was kind of forced back into the game by bad luck and Franklin is desperate to be anything but a hood rat. While Trevor never left the game and thrives in it because his anger issues are an aid rather than a detriment.
Violence for Micheal is a result of merely pragmatism.
Violence for Franklin is a means to an end.
Violence to Trevor is a lifestyle.
And the problems begin with the sort of game they were playing, especially with things like heists that require a lot of laser accurate planning, the right amount of ruthlessness (but nothing overboard) and, lets face it, a lot of luck. It just wouldnt make sense for Micheal and Franklin to do more violent missions and vice versa, at that point, why even bother having multiple characters then if they all act similarly?
It's always especially odd to me how they let random people basically push them around and demand they do odd jobs and these badass criminals just go "Urgh...fine, whatever, I guess!"
Thats basically 80% of mission cutscenes in the GTA franchise, I almost think they are somewhat self aware about it.
Besides we are usually controlling hired hands, not leaders (with the exception of maybe Tommy Vercetti). Nearly all of them are just taking it because they are thinking about the payment and reward.
