I agree with almost (if not) everything on the list here. But I think that Zen Cactus is a bit too OP. Her Mystic Orbs have a 10 damage point increase per shot for 4 shots, not counting the initial one. Since a critical hit at full ammo is 20 damage, and max damage is 60 (at one shot left), she can KO All-Star and Super Brainz Zombies from full HP if Zen Cactus is at full ammo.
Also, if any of you don't know, Electro Pea is faster than all other Peashooters in the game, and Hyper just makes him even faster, coupled with the ability to jump really high. I doubt that Electro Pea is TOO overpowered, though, but maybe he might be considered a tad OP because he has small hitboxes, he's fast, and his attacks deal some good damage, as well as being able to manually detonate the attacks while they're flying through the air.
And most Fire-inducing characters (ESPECIALLY Lil' Drake, Lil' Drake's Z-Mech (to an extent), Paleontologist, and (the worst example of all) BBQ Corn (who is able to fire off rapid shots which ignite the victim, and has a TON of ammo)) are also very OP, due to the fire damaging enemies over time. Plus, is it just me, or do the Zombies (Imp to name one of the more notable examples of this) perform better than the Plants?