Yeah I think you may have missed a skull match as you said.
I've played a number of matches with him (only at legendary) and haven't had him one shot anyone. I'd be curious as to what team you're using him in.
I've slotted him into, what I find a fun Explode based team.
No counters, so is risky and relies on just blowing up stuff and doing team wide damage. Can use mercy instead of Skullbeard for a faster start.
Enraged is nice for extra damage on skull drops to proc the Firestorm earlier.
I hadn't noticed the boost ratio text and agree it is slightly confusing considering considering himself being enraged is the only condition.