For all the use melee is in a game with long-range weaponry, it'd be a waste of time having different fighting styles.
Which is true. But it's those small things that make a huge difference. Now gameplay wise the charecters just feel like skins.
The number of "finishing moves" in the game add a lot of variety, though; you've got everything from a punch in the balls to a Glasgow kiss (look it up) to straight up slapping someone so hard they're knocked out, and so on.
All charecters do those. The only real unique ones are with trevor.