They're just upgrades of the other mouths, though, aren't they? Each tier has both herbivore and carnivore mouths. But this would mean that once you reach level 4, you could basically roll all over every other creature on the planet, except the ones that are also level 4. I mean, having different damage ratings for different mouths isn't such a bad thing, but twenty times the damage?
Come on now.
It just sounds like the creature stage might turn into one of those RPGs where after you've level-grinded enough, you go back to area 1 and fight those 20 HP slimes, hitting them for 8000 damage a hit.