Balancing that needs to be adjusted

Kinda agree for all plants nerf listened except vampire.
At the moment Metal with the damage increase and sunflower pot cooldown reduced seems more a safe and solid choice. 
Vampire is mostly overused by girls because she looks pretty..  and this is the most reason why i use her and stuffy...i think you overxaggerate a little bit here as to stand the metal increased hp need to continue shooting while fighting, and this being much weaker to burst and harass. Seems a high risk high reward pick and even funny to play, that's it.
By the way as far as i know vampire flower and fire flower didn't got a buff.

For the zombie nerf list i almost think that you just generally hate them...

Imp size couldn't be really bgger, but to compensate that citron splash damage, rose homing and corn accuracy has been improved.
Recently i just killed many of them without even aiming, using the no-scope aim and seems their hitbox is much more bigger when jumping. His "stated" opness is more like the fact that his double jump and gravity grenade at close range makes a frustrating experience, a frustrating experience is different from a op one, otheriwse i think PeaShooter Hype needed a nerf for the same reason.

The Mech cooldown was decreased to make you swap character from little drake and cone imp to another one (shrimp and stock imp, that besides the bias seems very balanced) and consider time snare and empeach being more often Mechs become much more manageable. Their big hitbox quickly being destroyed as long as a Peashooter or a Sunflower rooted themselves.
I never had a match with more than 3 imps anyway so i'm not sure if you just hate them or you're right, but i would appreciate a limit to called mechs over making the class useless.

Captain Sharkbite is not overpowered anymore, they reduced both his splash damage and his direct hit, and he already had a bad rate of fire compared to regular, He still has good accuracy but the lack of damage is quite heard. The only ability that could deserve a nerf is the parrot,which anyway, even with 20hp dies as soon there are at least two roses.. or an electro peashooter.. but whatever. The barrel is not op, is just a way to make him less defenseless. People complain about him being very good at close range, but the shotgun has very low range and make him much vulnerable to low-mid one, he has not teleport or hero kick, he has a good damaging shotgun, but his skills doesn't acctually work with it, so even if he has a very good shotgun, he can't really use that much against close threats like chompers and citrons (is not enough strong to deal with them).

Scuba seems more strong than Tank Commander, but this only before the reload upgrades. Scuba has not two reload upgrades and after two shoot even with one reload upgrades he has to reload about 1.5 seconds.
Tank Commander post reload upgrades, make is reload SOO much faster (little bit more than 0.5 seconds and less than 1, maybe is 0.75) that is almost in pair with Scuba Rate of Fire, and this is without reloading after two shots, but anyway Tank didn't deserve a nerf though, as peashooter compared to the first game are much less for counters when gaitling and since Foot Soldier kit is almost useless in this game (worthless smoke grenade and not many rooftops to camp) make him not that good character, so at least he should have very good daming variations.

Park Ranger seems ovepowered but only if you stands in his clouds, as long as you keep moving you dodge his entire dps, also i could be wrong here but upgrades on stiinky clouds seems not working or got nerfed because i remember those of Park Ranger being much more stronger and larger , but not totally sure.
Also i think Park Ranger doesn't need a nerf as he's a good counter to citron actually. 

For the Tennis Star, i think he is in the same position of the Fire Chomper. People mostly thought he was op because he was a zombie. If he deserve a nerf i think at least their class could be improved. Offcourse i think the same of Fire Chomper as he outclass every breathe chomper, so if he deserve a nerf, other bad variations could deserve a buff to compensate

Enginner seems not being played a lot and i think everything is fine (?) they also reduced stun grenade duration compared to the first game, which imho was unnecessary, this was made to not make the stun-grenade / turret combo being too broken, but i think this could have been solved with just make a cooldown between those. For being a support now is much more weaker compared to rose crowd controls.

For the scientists nerf sorry but i completely disagree, and being disgusted, the reason why you see again the trio is just because they are the only decent scientists that working good as assassin, and those ranged variations are just bad and can't really outrade anyone at any range and not really being helpful in that mean compared to a sunflower ranged weapon. If anything need a change, it's a nerf revert for marine and chemist that was quite manageable compared to zoologist.  Overall the chemist which lacks pointblack damage, but whatever, community ask, devs answer. 

Character thats need to be buffed 

Roses.. thanks godness is being shadowned by Citrons. If Citrons didn't got this unbeliavable buff we had the Rose Army back again and people would eventually complain more.
At the moment is much more better as supporting compared to Enginner thanks to damaging increasing (or more the ability to do them with homing being good again) and very long crowd controls.
Chomp thing could deserve a Hp buff to 150 for me together with a damage buff.

Six Shooter has two reload upgrades, a single buff could make him too much toxic to deal against (he's already a very good character).