Everyone in KOTOR does pretty much the same thing. Jedi are more powerful than the lot of them. Which means you dont have much in the way of variety. KOTOR II tried , but in the heat of battle it's not particularly noticable, or combat isnt touch enough to make it worth while(take you pick).
In D&D everyone has a role and no one else can really fill that role in quite the same way. That is what gives BG/IWD combat the edge. It's how the whole works by combining the parts.
Where as in KOTOR you just pick your favourite NPCs because the classes all do more or less the same thing and you have serious skill overlap.
To get really good combat you need to have a defined role for each participant. Too much overlap invariably means less interesting combat because you dont have to worry about making up for deficient characters. For example in D&D low level mages need to be kept alive and that forms a big part of the combat strategy as does their ability to clear a room by pointing a finger. In KOTOR a Jedi can clear a room by pointing a finger but has no particular weaknesses.