Once again you point out conditional factors as your argument against a general state of affairs. The rarity of shield using builds speaks for itself. If you're going to do less than 3/4 the damage because you have a shield (not to mention carrying the weight), you should have an ac that is higher, NOT just 4 higher for 10 rounds, but higher overall, all the time.
Do you honestly think +2 ac for shield users is going to break the server? Really? If so then I think you and I have reached the point where we're not accomplishing anything by continuing to speak to each other.
It is 10 turns, not 10 rounds, and they do have higher AC consistently,
all the time with an enchanted shield, and considering a two handed weapon user in full plate only gets +5 parry ac at level 19 without the use of magic, assuming 12 dex and gloves of swordplay, a shield user is very likely to have an enchanted shield by then, which also gives bonuses to saves, discipline and concentration checks. Furthermore, it is not about breaking the server, but about balance. I personally don't think giving shield users access to 2 more points of AC via feats is necessary to make them relevant, nor do I think it is healthy for the server balance, for the reasons I stated.
As for the "rarity" of shield using builds, I certainly don't agree with this. I can easily list 10 characters that are level 15 or above and use shields from memory: Lupinus Linus, Zidonne LeFebvre, Bastian (Can't remember his last name or even if he had any, a RDD played by Mika) , Zachary Dalensbane, Cyrus Gallant, Sieglinde, Marcus (He is a paladin, can't remember all the details again, I believe he is played by aprogressivevist though I am not certain), Samson, Katraka, Vjaya, Schala Wintermoon . And these are just 10 names that I can conjure from memory and my own character, and all characters listed are either active currently, or were active during the last year. It is really not a rare thing at all, definitely not as rare as you make it seem to be.
As for accomplishing things, I am trying to explain my point of view and why I think adding such feats is, in my opinion, not a good idea. I don't see why we can't accomplish anything if my ideas are contradictory to that of yours, I would even argue that contradictory points of view are helpful to accomplishing something. IF we have such contrasting viewpoints on the issues, it is likely that there is a compromise that can be found in the middle. So far, from what I understand, your points are that shield user deal less damage than two handed weapon users and dual wielder, and should have a
higher AC all the time. And as I pointed out before, they do indeed have a higher AC
all the time. As for the damage issue, I would love to see you break down the difference in damage and explain why you think that difference varrants a further increase in AC for shield users.