Can I ask where you're getting 6.25% from? My calcs is 18.75% failure to cast in one action. Feel like I'm missing something.
If the game was just about killing critters, then sure, might have to make it harder. Critters are dangerous in numbers and Conjurers can make more of them. Striking in combat let's you take a couple out each turn without worrying about AI.
But saying all this, what critters are good for is killing enemy minions. Not surrounding the Wizard. Critters are there to get your big minions down the board.
Tbh I think Death Wizards are over tuned as they can raise more zombies from the bodies of the tavern clientele.
I made this game in about 20 hours. So tuning and testing is still needed. I think I've done pretty well considering. 😁