You are incorrect.
Here you can read, better threads out there too. You'd be correct in saying that quite a low amount of AC helps against many PvP weapons as well, however, there are things such as pets, MA fists and maybe
this too that higher ACs should help against. Also, with high HP it might be useful versus SA, since SA checks AC's.
You'd be correct in that ACs could use some sort of slight revamp though to make them more useful, as they don't really come into play that much at TL7 since the expense is more useful things. But then again we have ridiculously big AC buffs available for some professions...