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I think you play in a very different metagame - a Grizzly (even a pet) is focussed down in 1 round or 2 - they are easy to kill.
You are probably correct about the different metagame.
And if my opponent focus everything to kill my pet grizzly (with 2 acid balls, several melee atacks and probably a rock or boulder), all the better fro the birds. If my mage's 5th turn is acid ball+bird (or bird+basic melee attack if opponent didn't bring armor yet), and my opponent spend his 2 actions for 2 acid balls or rust+acid ball on my grizzly (as well as his creatures attacks), even if my bear is going to be hurled a rock/boulder at next turn's first quickcast all my opponent actually did was giving my birds more time to attack him.
Both times I used this strategy against a zombie necromancer, the necromancer died before the big creature, and the game ended on turn 6 (before I finished attacking with all of my creatures in that turn).