Well the thing with biotic characters, is that its quite possible to have a wide variety of mentalities and approaches to combat and still have a class that would not be considered fitting for them.

Thane is case in point. He is technically an Adept, but he acts like an infiltrator most of the time. Don't get too hung up on what class your character is, as for the most part the class system is not so much a lore thing as it is a power selection thing. Just because you're a Vanguard doesn't mean you have to charge into battle and be a melee brute. Just think of it as meaning that you are a close quarters trained biotic instead.

By the same token, other classes should not limit a character. When I make characters for Mass Effect, I prefer to make the character first, and then apply what class I think their style best, as this is all more about who your character is than what combat niche they may fill.