Well, I actually now have been changing my fanfics to go to this where Chomper is able to hunt mammals (which could be big) and fish (which could also be big) in addition to non-saurian bids (and not the Petrie types either). He also eats insects. And, when saving Flatteeth, as he does sometimes, he sometimes has to protect himself from angry Sharpteeth, and sometimes he's killed those in self-defense, and, since they are dead, eaten those too.
That kept him alive and well enough, though his health wasn't the best, till adulthood. Around then, he noticed that he wasn't that full, but kept ignoring it, reminding himself that he could never hunt Flatteeth as Littlefoot saved him from drowning and he also was friends with Ruby and the Gang of Five (that should be a motivation not to do it.)
Anyway, the film could have referred to Sharpteeth in general, as Chomper could well be the sole or nearly the sole exception.
We already know Ruby busts the two kinds only and the cannon of the first movie as she eats both Sweet Bubbles and Shells.
Also, even if Struthiomimus is considered meat eater, Strut breaks that with his green eating, even if Ozzy only eats eggs.
Anyway, back to my idea, Chomper would not have the best health, and would get sick more than other Sharpteeth, but would be willing to accept that. He'd also have to take a lot of flak from practically all the Sharpteeth for not eating Leaf Eaters, which seems to be considered normal. (Both the narrator of the first film and Thud's laughter at Chomper's friendship with Ducky proves this.) Also, practically all Flatteeth Chomper saw in the Mysterious Beyond hated him as "evil" just because of what he was, and never thanked him for saving their lives.
Eventually, situations transpire where he ends up back in the Great Valley (he'd left years earlier after Red Claw seemingly had died).
There is some villain in the dino world who is conspiring to take over the world. He plans to use racism to divide the dinos (minus Bothteeth, because he thinks their superior diets make them worthy to rule the whole world.) and also he plans to control the Leaf supply, hence being able to tinker with the Flatteeth population, and, indirectly as Sharpteeth almost prey just on the Flatteeth, he can control the Sharpteeth too, and, with both those kinds under control, can push around Egg Stealers too. he'd have minions from all four kinds though Bothteeth would be the primary group behind his regime plot.
Anyway, I won't blab too much about my fanfic, but I will say that he wants to kill herd leaders too to help him move his takeover and also smooth talk his way into getting control of other food supplies.
The villain would be terrified of Chomper, not because he's a full-grown Sharpteeth, but because his diet makes it so that he couldn't be controlled by the plot to control the Leaf as it wouldn't affect him if he never ate a Leaf Eater and avoided eating dinos. (In short, his difference to everyone else turns out to be an asset!) Also, he's afraid as Chomper is teaching a female that Chomper is fond of and she growing fond of him to also start to wean herself off of eating dinos, and fears, if he continues enough, that he won't be able to control the Sharpteeth.
Also, Littlefoot is a threat to the villain as Littlefoot is an antithesis to racism and everything if ever there was one in the dino world.
In short, the villain wants both Littlefoot and Chomper DEAD!
Eventually, he sets Chomper up, Chomper accidentally kills someone, and Chomper has to run and gets away, with the help of a very confused and conflicted Littlefoot.
Anyway, Littlefoot gets banished for refusing to help the Great Valley go after Chomper. The villain also accuses Chomper of doing all the bad stuff he's done. Everyone believes him, thinks him so bright, as he kept giving warnings about Chomper, and he ends up slowly taking over the Great Valley, including its food supply and inflaming racism there, getting the remainder of the Gang of Five to fight each other even on racial lines for a while.
Eventually, Chomper does get wind of the villain's plot, but, as practically all of the Leaf Eaters (including the Gang of Five) have turned on him and most Sharpteeth too, he is tempted to just stay in hiding and watch karma bite both groups in the tush for how they treated him, as, after all, with his new diet, he can bypass the trick and go on.
Eventually, though, Littlefoot and Chomper team up again and drive out the villain. All of his henchmen, which are many and cross many kinds, get a very stern punishment: having Chomper hunt them and their kinds, which he does.
So, Chomper does ultimately end up eating dinos, but is allowed to stay in the Great Valley and have a family of his own and live happily ever after.
My fanfic is ultimately a morality tale where Littlefoot, even if he is so different, turns out to be a hero worthy of leading a herd and Chomper, despite being mocked his whole life, ends up saving both Sharpteeth and Flatteeth.
It's interesting that older Chomper looks like a monster, whereas the villain looks like the type of guy everyone wants to be (at least before who he REALLY is is revealed).
At the end, it's actually the villain who's actually the REAL evil Sharptooth and murderous killing monster whereas everyone finally sees Chomper for the hero he is and stops caring that he's a Sharptooth and may not be as pretty as he was when he was a kid.
I think the theme would fit in well with the overall theme of the LBT stories and would be a great finale for the series itself.
So, a Chomper making it still scenario is still plausible, as difficult as it might sound, I just made one that could work.