Tahm Kench's Devour

So, playing a game earlier, I noticed something. Even at level one, Tahm can chunk someone's HP bar, by spitting minions at them. Like, heavily. It's some really, really sick harass. His cooldowns and mana costs for doing so are roughly just a bit higher than Galio's Q. The base damage is higher, however, and it has the same AP ratio.

My question is.. Why? Why is devour, something that already has a TON of utility, outside of spitting lane minions at your opponent, so goddamn powerful, straight out of the gate?