A high level fighter should just be death incarnate to anything more than a level or two below them. Just, every attack is like 'save versus death' and every time you try to escape or cast a spell in their reach it triggers two AoOs and an ongoing penalty. Imagine being attacked by Muhammad Ali but he's twice as powerful and carrying a giant sword. It would be utterly overwhelming. All of these '+2 to this' and 'have your second choice fighting style as well' type bonuses are just too small.