Fixed values would help the Shepherd a great deal, making it as tactically-minded as the rest of the characters.
Well, the War Machine is a Doomguy-esque Solo-able slayer, I'll give you that. Rip & Tear wasn't immediately clear, I admit, but after looking up Creeps in the rules we got it right.
About the Sorcerer, maybe letting them change Chain Lightning or Fireball with each Rest, or putting up a limit where they can't deal the same damage type would enhance flexibility without breaking balance.
I'm looking forward to Demon Crawl future developments, and I can tell you I'm not the only one. If I manage other sessions, I'll get back to you.