Mary Marvel, trained for three months by Lady Shiva and Cassandra Cain, felt confident enough to take on a zombie Wonder Woman, and lived to tell about it! Mind you, she didn’t kill Wonder Woman, just stun her enough (and seemingly breaking at least 1 wrist) to allow the kids to escape.
So I guess this brings up the idea of how lethal Shazam, or Superman, could be if they trained how to fight effectively, as opposed to relying to their powers and invulnerability.
From – DCeased: The Unkillables #3