They should not be needed in the first place. Even if you agree that the Avenger was overpowered with an extra 2 AC, then the Avenger should've been built this way from the start.
Oh, I agree that it would be far better to have everything perfect from the get-go. But in the absence of that happening, I think it better to fix mistakes rather than leave them in place!
When you look at something like this, you can't also go and say, "But they can't foresee every problem," because it's not like this was hidden or some sort of CharOp monster. Much like taking Fullblade or Execution Axe is a must have for the class to be on par with other strikers, taking Leather Armour Proficiency was a staple.
I think you vastly underestimate how much a product can change through release, and how easily it ease for small unintended elements to slip into it (like writing a class feature to help cloth armor, but it ending up working for all light armors).
Would I love it if they caught all the problems before hand? Yes, absolutely. But not fixing the problem when you have the capability and the knowledge of the mistake, that would be genuinely frustrating behavior. This isn't ideal, but it is a vast improvement over what you seem to be suggesting, which is that once something is printed it is set in stone, no matter how much it breaks the game.
What makes this particularly painful is that the barbarian, an already powerful melee striker class with more options and more damage than the avenger, just got a massive AC boost prior to this avenger nerf. That shows a distinct lack of consistency in their review process. They obviously have no yard-stick or else these two classes wouldn't have such a large disparity between ability. Barbarian is clearly the superior of the two.
Oh, agreed. I'm very bothered by the recent barbarian AC boost. I'm very hopeful that it will be addressed in the next month's errata, when they will be dealing with primal power and other recent releases, as this errata dealt with prior projects.
If they leave it as is... well, I'll be upset at what I see as poor game design on their part. But leaving one broken element is not an excuse for allowing others, and I'd much prefer they fix 5/6 things I feel they did wrong, rather than leave them all in the game indefinitely.