How does this make sense?

meet galio

Go ahead and take a look at his info if you're confused.

http://gameinfo.na.leagueoflegends.com/en/game-info/champions/gragas/

140 + 8% of your max health will hurt like a motherfucker, even if he doesn't build AP.

He has high base damage on every spell and builds Runic Echoes to further increase his early game damage (but he trades this for tankiness). Literally single negatron cloak halves his damage because in most scenarios he has zero magic penetration. His damage is even bigger if you let him wombo combo you (knocking you back to fully stacked Q with E or ult etc.).