this does not bother casters as much
An extra enemy mob attacking your 1 defense mage bother casters a lot more than it bothers melees with 3 defenses.
Think of it as a balancing feature for the advantage of playing a melee.
You guys think guarding ranger mobs are hard? Wait until you play a 1 defense mage and the freaking ranger pets are CHARM IMMUNE and can't be put to sleep. And to rub it more, they all have a freaking vuln that can be exploited by melees attack.
And then they wink back at you with an ICE resistance...
Let's play a DK and either use Iceball to harm the master, or Fireball to harm the pets and scratch the master.
Rant apart. The best would be to change the guard message so that it states that the pet jumps at you deflecting your blow so that you miss your target.