It will make the problem even worse. Suddenly you will be able to PA to your hearts content against all opponents regardless of their AC.
At least a normal barbarian would simply dump all he can in power attack and count on killing most things before they can even hit back.
If I was playing the fighter/barb it would mean even more use of PA. Note that there is a tactical feat (Shock trooper) in CW that allows you to this, but only when charging. So at least WotC thinks that the trick is worth a couple of entry feats (to even take Shock trooper) and should only be an option in special cases.
If you do the math for PA you will find that its not really that effective. It only really shines when fighting low AC, high Hp enemies.
And of course most fighter types (including multiclassed and barbarians) will end up with that feat.
1. it opens up a lot of juicy feats like cleave.
2. There aren't that many good feats for a fighter to take, and some of them requires high int, high dex etc. PA requires just high str and most fighters has that.
And if fighters dominate most battles IMO thats a good thing. Its usually the only thing they are good at. As soon as the game deals with other things than combat fighters contribute with ....nothing.
And if you are dual wielding great scimitars (khopesh ?) with a less than full BAB character and can still hit your enemies I'm thinking the biggest problem in the game ain't PA
