The OP is very much right about the things he posted. High AC and low AB makes you useless, unless there is aggro in the game.
Most DM's I played under do use some sort of aggro system. For as far as the creatures are capable they assess how dangerous each opponent is and go for the most dangerous one. For dumb creatures this is usually the character that hit it hardest.
Sometimes we faced a hit and run challenge where they simply try to take out the weakest party member and then run away.

Adding/using abilities to make people attack you can make AC-builds viable, but be careful because it can make combat very easy very soon. (In other words the ability should only work about half the time or less)