Sorry to quote just you, but it is tiresome to me when people start getting on a soap box (not saying you) and start saying you shouldn't do "X" because that is exploiting mob AI then they go and shield block a door and watch the stupid mobs cook in the firewall and don't hesitate at all.
All I know is the Devs put in collision detection so that mobs can't pass through players, to me that means any kind of surrounding/blocking/walling is part of the game design period. It wouldn't be that hard to add some logic to the mobs to say, path to my target "X" is blocked, attack nearest guy "Y" instead for the next 10 seconds or until dead regardless of agro list.
Maybe they have done some of this I don't know.