Who cares. It's a fun action movie. Not meant to be a drama. If the characters were worth mourning they wouldn't have got themselves shot

Harley probably was trying to shoot Marlboro in the head and shot him in the arm instead, then he got Marlboro to shoot Chance's phone and Chance, hoping Chance's goons would shoot him first. Harley is an as a55hole friend.
BTW, was the whole broken boot thing just for a way to kill the boss?? Lol

Yeah, that was one of the things that really bothered me about this film.

True. While Marlboro did express some remorse, especially in Las Vegas, Harley seemed terribly callous and indifferent about the fact that it was his lousy idea that got some of his best friends brutally killed, and left Jack's wife a widow.
I guess the whole point of this movie is that Harley and Marlboro are not really good guys, but rather anti-heroes. Two outlaw dumbasses who can't get anything good done right, despite their best intentions with the bar.