I had a character I rolled up and sadly never got to really use. He was a 4e Blackguard, optimized to nova as often as I could get him to do it, and nova hard because he was a striker character.

But he was very flawed. He was a blackguard of Fury who abandoned the worship of Gruumsh, the god of slaughter, for Kord, the god of storms (in 4e, at least). His flaw was the fact that he was literally a ticking time bomb of rage.

So you can be optimized and still have a flawed character. Flaws don't have to be physical or stats based, they can be very deeply personal flaws. A character who can't approach women because he's shy, or who hates children because he was abused and he's afraid he'll abuse them just as he was. I would say that if any of Shakespeare's tragic characters had stats, they'd have very good stats. Hamlet, for instance, would probably be a great swashbuckler with a kickarse bluff score based on how he duped those pirates, but he was obviously a very deeply flawed character!