Choose sides. This absolutely needs to happen.

Here's how I'd do it... It's something I've been thinking about lately as I understand your frustrations very well... This happens in all modes regardless:

• Players get to choose their preferred role before queuing.
• If there were more plants than zombies, then the system adds "10 % bonus coins" to the zombies side and it keeps increasing it if there were players waiting for others up to "30 % bonus"
• You can also pick "Play Anywhere" and always get "30 % Bonus Coins". This will place you in "any" game mode where there are fewer players to fill the space and you will only get your 30 % more if you finished the game. (Except for maybe... Battle Arena since it needs a different kind of dedication and mental readiness.. Unless it's just me who takes it too seriously.)

This way, people who contribute in filling the gaps will be rewarded with "bonus" and "extra" coins while others who have preferences and always want to stick to a side no matter what, they will get the usual coins with no bonuses or extras. Notice that I have emphasized on Bonus and Extra because you're actually not getting penalized for picking your preferred side, you're just losing a chance to get more coins. (It's up to you how you perceive it though!)

I personally prefer "attacking" in Turf Takeover since most defense teams refuse to contest on payloads/points while I do most of the job. What irks is when half of the team is around the objective, especially after I die trying, when it's overtime and they just don't bother stepping on the objective at all... All my 2k objective score worth of effort to prevent the objective from being captured gets thrown into the garbage bin due to teammates thinking that someone else would step to contest. It does happen the other way around too sometimes, but at least when attacking I have summonable allies that can assist me... Thanks Hypno-Shroom, you are better than some teammates =(