I like it! Though ideally, each class would be equally useful in a way that they work best if you combine them, making use of all the unique perks offered by each "career".
For example, maybe the Heavy does get the largest gun and the best armour. But he's going to be slow and (relatively) inaccurate, and other gangers will have to make up for that, making sure the enemy does not hurl too much firepower his (or her) way, and picking off individual targets that are too dangerous to be left to the Heavy's "spray 'n pray" gun.
The Heavy will cover their gangmates, and the other gangers will cover the Heavy, all depending on the situation.
Good analogy regarding the Juve, by the way! It escaped me earlier, though it's so obvious.