I would probably ban it in my games. Adding con to AC should be a class feature, a tradeoff with other powerful class features, not a simple feat that really allows some min-maxing
If 80-100% of the CO builds are using something, it deserves a very very close look at.
It should have been a class feature for barbarians to add Con/Cha to AC, instead of Barbarian Agility, and the feat would never be needed, and no one would have complained from the start about any AC issues with the barbarian.
So you ban ranger's twin strike?
So it's a stealth-errata with a feat tax. Nothing world-shattering.