Personally think Erebus is an overpowered demigod.
I shouldn't be able to take down a Rook in a knockdown, drag-out fight. I also shouldn't be able to out-kite a Regulus.
I can do both by taking Bite to completion, his coven to completion, and fill out his stats and leech aura. Get his Bat teleport for survivablitity.
You are now Mr. Hit-and-run as bite has a ridiculously short cooldown for a leech, and his minions are good distractions/DOT. bat teleport away from any stun animation and you can take down three demigod in quick succession. Only problem would be a mirror match or a Frost focused TB.
Note I ignored his stun. I only took it if there was several generals, no real point otherwise since again Erebus focuses on hit and run.
Generals as a whole are great late game, assassins are good rushers. There is of course a wide range between those poles where the actual demigods fall.
Personally didn't see the point of the Oak, but I can see how some would like him.