The Chomper is already very powerful, especially up close. And people fear him.
The main problem is not his damage output (ever thought about the Fire variant?) but his standing on the battlefield, where he is an easy defenseless target everyone hates. And since people tend to go after the easy targets instead of the challenging ones, the Chomper is in the focus pretty fast. And to top it off many people play the Chomper wrong, ultimately leaving the wrong impression.
So as experienced Chomper player i can say the Chomper needs more health. That's it. 25 more HP should do it. That would bring the Armor Chomper to 250 HP . Even 261 with the upgrade. Not to forget the Armor Chomper already has 50 dmg bites.
The rest depends a lot on how he is played. And no one wants masses of rushing Chompers going solo on the enemy team. Which of course is often the cause of death after 1 kill.
Right now we already have important changes affecting the Chomper in GW2. He is a powerful tool to burrow behind enemy lines and disable machinery. He can nullify the twister and barrel blast. He can trade some health for a burrow on an active twister. He can lock campers in place over a long distance so the own snipers can take care of them. Not to forget how powerful goop in general is. Goop only lacks the 35 damage it could deal in GW1 as cheese type.
His main problem is just that people like to shoot defenseless targets. And that is the big Chomper when he digests and also in general. But it is necessary to balance that insta-kill out with a downside. And it is not simply an insta-kill as the victim ends up unrevivable. And especially the unrevivable status effect is something only one zombie class has to offer now: Cozmic Brains. But only under certain circumstances that are not guaranteed to happen.
And even more changes have been made. Thinking of the annoying respawn exploit that plagued the first GW. Or the broken ZPG animation that made rockets go off inside the chompers mouth, killing him in the process and freeing the victim. Those times are over. Now he can even devour an active Impkata Imp. Which is hilarious to watch anytime by the way.
The only thing i don't understand is why he does no longer get XP for removing armor from AI zombies. And why he can no longer remove armor from AI zombies with a spikeweed. Not to forget why the zombies no longer hang in the spikeweed. Which was a really nice animation.
Gameplay wise one of the major problems he has is the randomness of a chomp that replaces a bite. That way a melee battle can lead to death as soon as the grab animation begins.
In addition the Chomper should have the unique ability to be marked for a shorter amount of time, to increase his stealth capabilities behind cover or while burrowed.
Teamplay wise i miss something crazy to happen when the Chomper manages to eat a goat. That's clearly a missed opportunity.
So careful with the demands of buffs. Even if a Chomper dominated game would be something to watch. It would ultimately ruin the experience just like Rose did.