While this looks decent it takes a long time to get to this level, while a str. based fighter can dish out as much or more damage in the first few levels!
Well, let's see it then. You didn't say anything about 1st level, which is a somewhat different comparison.
You didn't specify the order of feats. but I guess you took weapon finesse and TWF first along with Weapon Focus. So that's +2/+2 1d6+2/1d6+1 at first level. Not bad if you're fighting kobolds with 4 hps, but against tougher creatures a two-hander will consistently do more damage despite losing the 1 attack, and with Cleave can kill 2 opponents per round.
So, Power Attack and Cleave? Cleave is nice, but you have to hit, and there has to be an adjacent opponent, and it only works on a felling blow, and you still have to hit. On the other hand, two weapons has a good chance of wounding/killing two kobolds or maybe even two orcs, every round. And the Dex-based fighter has (likely) a better initiative and a better AC.
Hmm I'm trying to reverse-engineer your stat array but I ended up with 27-point buy which is beyond epic fantasy... unless you already added the bonus from the belt, in which case you have +1 to damage from an unknown source. In that case 18 PB is not too bad, between standard and high fantasy. Of course that makes the character even weaker on low-levels, with just 1d6+1 damage/1d6 damage until 4th level.
Somehow I got in a hurry and messed that up.
Try: Base stats Str 14, Dex 14, Con 14, Int 10, Wis 14, Cha 10, +2 Dex (human), two advances to Dex. Final Dex 18. Everything dex-based goes down by 1, the change to Str is inconsequential.
Reversing Str and Dex, the Str-based fighter would have Str 16, Dex 14, Con 14, Int 10, Wis 14, Cha 10, at first level. Greatswords would be +4 melee (1d12+4), with power attack, +3 melee (1d12+7). On a hit, that averages 13.5.
Shortsword +2 melee (1d6+2) and +2 (1d6+1) on two hits yields 10. So in a full attack situation, the difference is quite small, even at 1st level. The two-hander can certainly do a lot more damage with a standard action, assuming no power attack and both getting +4 to hit, 9.5 versus 5.5. However, the Dex-based fighter still has +1 initiative and +1 AC over him. Unless you are fighting a low AC, high hit point foe with a relatively poor attack bonus, I don't see the two-hander has a notable advantage. Cleave is useful, but being in contact with so many opponents just makes the lower AC that much more of a weakness.
As for rogues and rangers, rogues have to burn their sole feat at 1st level to go TWF and have a lower BAB, meaning a double whammy in terms of accuracy. Unless a ranger is fighting a favored foe, he will be in evey way inferior in melee to the fighter at 1st level.