My arguement was Duel Wielder has +1 AC. It's there in the feat. But until you max your Str, you're giving up to hit for AC, which MAY be good for your build, but it's not a decision I'd make.
I have a convoluted spread sheet. I haven't gotten to Barbarian yet; I've mostly looked at champion, assassin, and devoted paladin; I've looked at the ranger a little. I don't take advantage into account, but I test against monster default AC which nets a 65% hit chance if you start with a 16 Str or Dex and increase it at 4th and 8th. I haven't tested feats because I'm currently trusting that the feats are reasonably balanced against ability score adjustment to primary stats. This means my numbers are off post 8th level, but that's fine for me. I'm just eyeballing the classes to help me with making variants and new subclasses.
I keep hearing people say that TWFing is a Dex thing. Nothing requires it to be. Str can TWF just as good as Dex, and there is a trade off between AC and Stealth/Initiative and Str/Dex skills and saves. But then again, I think there should be two-handed finesse (non-heavy) weapons, so I'm in the minority on that one.
Since both Str and Dex can use the duelist style, I think they were meant to be even with each other, just a little different.