Unbalanced Characters

Compared to Garden Warfare 2, Battle for Neighborville is pretty decently balanced because they've completely eliminated the elemental variations of the different character types-- which I'm sure made GW2 absolute hell to balance properly.

It sounds like you're comparing Oak directly to the Imp's Mech in that the Mech has a fuel based timer and the Oak doesn't but that's not the correct comparison.

The Acorn/Oak and the Space Cadet/Space Station are a better comparison--while each has unique attacks both can transform into a larger "tank" based form and both can link with up to three other characters of the same class and neither operates on a timer. If anything the Imp and his Mech don't have an equivalent on the Plant team unless you consider that they are countered pretty effectively by the rooted versions of the Pea Shooter and Sunflower which are both more powerful in that stationary rooted form and can make short work of any Mech.

PvZ games like BfN have always had asymmetrical teams-- both sides either have roughly equivalent character classes or classes which effectively counter each other the way that the Engineer counters the Chomper or the Pea Gatling counters the Mech. It's definitely odd and a bit jarring if you're coming from games like Battlefield or Call of Duty where both sides have access to exactly the same classes, weapons and skills. It's definitely harder to balance but at the same time each unique class has a specific way you should be playing it and not all of the classes will suit everyone.

Back in GW2, when I first started playing, I thought that the zombies had an unfair advantage as well but once I got some experience with each class and figured out the best play style suited for each I stopped believing that and came to understand that there was a sort of quirky balance to the game. 

Granted, BfN is new so they'll be fine tuning the actual balance in terms of damage output, accuracy, range and so on now that they have a player base from which to gather data and they've changed some fundamental things from GW2 in some of the classes which crossed over and introduced four new ones so there's a whole new learning process in figuring out how to approach each class all over again and how to counter the abilities of the other side.

The problem with games like this is... it's so dumbed down that you easily can find out if you're on a team of morons or not... and most of these players are so bad, they abuse the characters that are usually pretty heavily lopsided to make them feel like they're good.

Take this week's game mode, Team Vanquish. You get points for kills, you take away points from the other team for revives. It doesn't take a * to figure out to stick together with a minimum of one healer... yet most of the games are so severely lopsided, you know which team had the morons running around by themselves going against 3-4 on the other team. This is the game mode where Scientist shines. He's still the strongest CQC character in the game thanks to his teleport (which really needs to be capped at 2 with a long refresh) and now his healing is mobile in an attempt to take him out of the offense, yet people still refuse to target him primarily.

@AWMaxSterling I imagine that BfN will have one of the same issues that I noticed in GW2; a larger number of younger children playing because of the amusing and cartoony presentation.

So it's probably less that you're playing with dummies and more that you're in a match with a certain percentage of younger kids. The older ones of them can be pretty good and team focused but not all of them are- many will just mainly bumble around because the game looks inviting and those ones will likely not even grasp all the controls and abilities let alone the teamwork and tactical aspects of certain modes.

Getting populated by a certain percentage of players who are probably not quite old enough is something that happens when a game is designed in such a brightly-colored, whimsical fashion that it attracts the attention of a younger audience.

I also have to add that the entire idea of this franchise is to be unbalanced. Its the crazy things that emerge from all the differences.

What people mostly complain about is when a character severely outperforms all others. Which then contradicts the asymmetrical design and turns PvP matches more into predictable scenarios with the same character being picked.

I have no idea how Popcap manages the player distribution in the background, but i hope its not based on level. If anything i would start at ensuring groups are equal on teams and go from there. 

In the end it does not matter how old you are, but a team of people just derping around because they got their attention elsewhere will underperform no matter what.