As a dm I like to target spell casters first and hold actions until the caster's turn. I never hear complaints from players that someone playing a certain class is overwhelmingly overpowered. I hear players complaining that my tactics are ruining their characters. the way I see it even the dumbest creature knows to attack the guy that's hurting them the most. Archers are second on the kill first list.
Focus fire on the character that can't take focus fire. If the tank exists, he is either up to the taunt requirement of avoiding it or the squishys die. It works well to disincentivize squishys from being remotely mortal.
This is good or bad depending on taste.