There's a lot of truth in this.
I had a game where the core of the party was decently optimized - an Archivist/Master of Shrouds (me), a Wu Jen and a Warblade. There were also a few other players that weren't there for every session, and so hadn't learned to work together as well as the three of us had.
The DM got very upset, because the Warblade (who had focused on AC, and did most of the mopping up after the Wu Jen would toss down a control spell and I would debuff enemies with my shadows) was basically unhittable by the average mook. He scaled his encounters up to compensate, but that made his enemies too deadly to the other players (who still hadn't learned to do things like stay on THIS side of Evard's Black Tentacles and coordinate attacks).
It ended up turning into a nuclear arms race, where the DM kept increasing encounter levels to the point where one bad roll meant a PC death. We were generally losing an average of one PC a session (and this was just getting into the mid-levels, so PC deaths were still prohibitively expensive to deal with).
The DM was pretty frustrated with the Warblade in particular, because the idea of rolling and missing against him 75% of the time just didn't fit with his style of DMing. I argued that honestly, the Warblade couldn't really do much else - the Wu Jen and I were doing way crazier things - and he'd sacrificed a lot of versatility to be that good at avoiding hits. Besides, even with his crazy AC, the Warblade still ended up close to death almost every session, since he was the primary target of most enemies.
It didn't matter, though. Even though he was an excellent DM in a lot of respects, he just couldn't really accept the idea that, if a character dedicates most of his resources to AC, enemies are going to whif a lot. In the end, the guy playing the Warblade retired him completely, after an enemy in the game stole all his armor and gear...