To me, they didn't really get away with more violence with Chomper. Eating a bug and biting Cera's tail with puny teeth isn't what I call really that violent. He's just a baby sharptooth after all. And plus I don't think anyone really cares that a bug is squashed on screen. It's not considered gory I don't think.
And even if you could say that they got away with more violence with Chomper because he's a baby, well that's the point as I already stated. He's a child and can't do a lot of damage. If they allowed a larger sharptooth get away with that, we could have seen a very graphic, as in seeing organs spilling on the ground or at least a pool of blood, from a victim, or maybe the sight of a sharptooth ripping into a bloody carcass. And a kid friendly scene this does not make, at least that's what they would feel.
I don't really think it was unfair that Chomper got to eat on screen or bite a main character on screen since he's just a baby. As I said, it makes sense. Parents aren't likely to complain about it. But had Universal done what you wanted, Bruton, and let other sharpteeth show more violence, there was the chance that Universal would have been sued by disgruntled parents.