Don't you think that game mechanics are integral in allowing freedom in terms of playstyle??? I'm not necessarily saying that playstyle variety for 1 particular character can't be done in other games, but that the "level" of variety, or as I've been saying "freedom" is moreso than in other 3d fighters... I'm a Feng player, and personally, I feel he's very good at CH fishing, rushdown, mixup, and turtling (which is what many Feng players have been doing since 5.0)...
You're exactly right though, specific game mechanics being gimped can definitely affect any character, and can either force them into playing their "role" or allow him/her to take on another style altogether...
As far as 2d fighters go, the only game I can think of that gives the player any type of freedom would be Battle Fantasia. The freedom doesn't work for every character (like Urs and Freed for example), but for the majority of them, you can play almost any style you prefer.
I would say KOF, but certain characters are a hodge podge of 2-3 gameplay styles, and when attempted, some characters can't certain things because of their weakness, be it a purpose-specific projectile, or moves only being beneficial in certain aspects, but not in others (Billy's hitboxes of his qcf+P and qcb+P come to mind)...
