Did/Do you feel that way?
I like TWF, but then I also play a lot of fighter/rogues and ranger/rogues. In my opinion, TWF excels when you have access to bonus damage dice.
I was just running some numbers and (before factoring in power attack)
That's a problem... but go on. You can search out the counter-arguments on Google.
the results I got showed that TWF with two short swords did ~50% more damage against a given AC than using a greatsword. So I'm questioning if I screwed something up.
Test your math by running it against the SRD TWF figures. It will be instructive. If you come to the end of your process and your numbers look right (a ~50% increase, which sounds right to me) then you need to seek out the counter-arguments that include power attack.
I am also curious if you did any such comparisons and, if you did, what results you got.
On paper, discounting power attack, TWF appears to show an improvement in the 150% range (158%, 147%, etc.) This is for the SRD.
The change in iterative attack bonuses and the gradual reduction of the TWF penalty in TB gives TWF a gradual improvement-- again, on paper, discounting power attack-- that improves to about 175% and eventually to 200%-- perforce, as one might expect when comparing a (0/0) attack sequence to a (0/0/0/0) attack sequence. (You don't need a math degree for that.)
Once you hit that point, most outside considerations go away, including power attack. You're comparing (0/0) to (0/0/0/0) on a level playing field. At that point all you can do is decide if the 21 DEX and 4 feat investment is worth it and "ok" at 16th level. (I reckon so.)
Well, in campaigns with both the BHS fighter and the TWF guy I have seen they both try to get an animated shield as soon as possible.
In my campaigns, the PCs don't "try to get" anything. There's no sense of entitlement just because someone happens to want to try out an uber build. They get what they get.