So let's take the standard Chomper in a theoretical 1v1 against every (standard variant) zombie:
1) vs Imp: The Chomper can easily deplete the Imp's life bar (which is only 75 points) with a couple chomps if he is gooped. You just have to stay out of range of his gravity grenade, or even bait it out then evade, goop him, then chomp a couple times. If he does the gunspin thing, you goop him then keep chomping at him. Believe it or not, you can actually eat the Imp when he is in that gun spinning move. So the Chomper will usually beat the imp 1v1, and you can even beat his mech if you surprise, goop him, then keep biting the mech from behind.
2) vs Super Brainz: Up close the Chomper can probably win 10 1v1's out of 10 against Brainz. His fireball you just dodge, bait out, or goop him before he fires it (then eat). You can also eat him (from underneath the ground) when he is in turbo twister, or you can goop him and eat him (while spinning) from above ground, or plant a spikeweed on him when spinning and it stops him (then free lunch). Chomper basically decimates him up close.
3) vs Captain Deadbeard: From far range you just take cover and it's a stalemate; neither player can do anything really. Up close I would estimate a 9 to 1 or an 8 to 2 1v1 matchup of these two characters fighting, in favor of the Chomper. The Chomper's spikeweed, if planted on Deadbeard when he is EITHER in barrel formation or the cannon, literally evaporates the barrel or cannon and traps him in the weed for a free snack. Of course if you try to eat the barrel or cannon, then that is a rookie mistake. All you do to him when on the cannon is stand directly near him then plant a spikeweed to capture him. If he is landing splash damage shots, then you can goop him (with standard purple) to slow his rotation, spin around him a little and plant it from behind. Spikeweeding an EXPERT Deadbeard when in barrel formation can be a little more tricky, but you can always goop then land it. Even a very slight juke move or walk around of the spike weed by an expert will evade in (when in the barrel) because the spikeweed DOES NOT lung forward at all when thrown out, but at best you can use it as a deterrent to prevent him from advancing, wait until he blows up and leaves the barrel, goop, then eat him. Other than Deadbeards two up close tools, you just goop and eat him.
4) vs Scientist: A head to head with the Scientist can be close, but I can pretty much just goop and eat him every time, unless he runs up from behind. Even if he does run up from behind, I can still beat him very often because of the health advantage.
5) vs Soldier: Pretty easy to beat this guy up close, you just goop and eat him. If you miss, you can always use the dig and you will encounter the same behavior from most average to high level players. They will wait until you get just underneath them and then use the rocket jump. You can actually bait this out, look up in the air to monitor where they land, then collect your snack.
6) vs Engineer: Chomper's spikeweed evaporates his turret and ties him up for a snack if you get close. You mostly have to watch out for his sonic grenade, but the Engineer is one of the characters that can beat Chomper in a 1v1. His jackhammer can be tricky to counter, but you just have to goop him and (standard chomp) from the front to kill him with strikes. Trying to eat him while on the jackhammer just eats his jackhammer, then gets you killed.
7) vs All Star: You can kill him virtually every time if you land a goop on him up close and eat him. If you try to dig eat him, players often wait for you to get close then football charge after that, but you can bait this. After the charge you might have to bait the imp punt, or freeze him with goop before he does it. If a person plants a tackle shield or starts facing the wall, there is a certain tech they use where they time an imp punt that they throw at the wall (or tackle shield) to bounce off the wall and kill you as you are coming up from the dig. The timing works, but you can bait this out if you see what they're doing. If you bait out that tech, they are out of the imp punt then only have their charge left. Even if they land that charge after a missed imp punt kill, you just goop and have a snack.
So just because a Chomper in expert hands will win most 1v1's doesn't mean he needs nerfed because he's actually pretty weak outside of 1v1's... It just means that it's bad to trade with an expert Chomper up close with alot of characters.