I don't think any of the characters are overpowered. Something can always take out another. You sound like you don't like the Pea because you can't kill it. Be a scientist. Learn to use warp, goo-blast the pea's face 2 times, or throw down some grenades, then warp out. It's simple, I find the peas are easier to kill than the 150 HP cactus or the over-healed sunflowers. When you get a group of sunflowers, boy are they tough!
I can kill Peas just fine and I'm sure others can as well. That doesn't mean they aren't overtuned.
This is true, but instead of complaining about everything you believe to be bad or wrong with the Pea Shooter, why not suggest some changes? Even minor changes (like doing 3-5 less damage for splash or direct hits) is more productive.
