Not a clear advantage. Just a promise: "If you really do the right stuff, you will be better t han the simple fighter". That's what I mean with "smart play". If you generally find the right stuff to do, know when to use your resources and when not to, know which combat maneuver is the right to perform or when to just make a simple attack, then you will be better than if you don't, and you will be better as the simple fighter that doesn't get these choices. If you only sometimes get it right - well, maybe you'll be as good as the simple fighter.
I dont find myself agreeing with this position. I have players of varying level of desire in terms of how much commitment to character mechanics they want to take, but none of them would want an option that is "simply worse".
My players just pick what suits there play style. This is where I have a problem with this position. Complexity has nothing to do with potency, its all about the experience the player desires. I dont want to say to my player "Look, I know you want to play the simple character, but understand, simple fighters are just meant to pack less oomph".
I think the more complex model will be more powerful simply by virtue of synergies and adaptability, but it doesnt mean I believe it should be that way. When you design, its about setting objectives and I think a "complex fighters should be better than simple fighters" objective is just not a good one.