Let's not beat around the bush, Taaannnk!! is the worst thing in the entire game.

-Constantly getting spawned out of bounds, was only fixed over 10 years after the mode was added.

-Getting spawned out of bounds and instantly killed on levels like Dead Center - Hotel over and over and over, this hasn't been fixed.

-Absolutely infested with cheaters, even more-so than regular Versus, it is impossible to play a full game on this mode without running into at least one obvious cheater with bhop scripts or speedhack.

-Tanks will spawn before you can get the bridge down on the Parish finale and the door opened on the Cold Stream finale.

-You're likely to get spawned far behind Survivors and never be able to catch up unless they're forced into a crescendo event like grabbing Whitaker's Cola or the wait for the ferry on Swamp Fever.

-Adding onto the previous point, Tank spawns are randomized, so while one team might spawn right infront of the Survivors and block their path forward, the other team could get spawned at the start of the level, essentially costing them the round before it's even started.

-AI Infected don't spawn if your team isn't full, unlike every other Versus mode in the game (including other VS Mutations like Riding My Survivor), meaning you're heavily disadvantaged on Infected side if you don't have a full team. This is especially bad as Tanks in this mode have less health than they normally do in Versus.

-Adding onto the previous point, AI Tanks will still spawn during the finale, on-top of any player controlled Tanks. This brings a new problem as holdout finales can be "softlocked" indefinitely by preventing the game from spawning the second horde. So long as at least one Tank is alive, the game can never spawn the second horde, thus by leaving one person far away from the fight, the Survivors will inevitably die or be forced to leave the game.

-Lack of grabbing infected (Hunters, Smokers, Chargers, etc.) means Tanks can get endlessly looped in certain areas like the Park in Parish if someone feels the urge to hold the game hostage for a while.

Now it's not all bad at least, they made a nice quality of life change where areas that normally require the whole team present to progress now only need everyone who isn't downed or dead to be there. This makes it such that levels like Hard Rain's Sugar Mill and Mill Escape, No Mercy's Hospital, Parish's Park, and Swamp Fever's Plank Country are theoretically possible to complete in a full lobby, where before it was virtually impossible.

I want to preface this section by stating that these are only things I think would make this mode a more balanced and fun experience for both teams. You can have a differing opinion and that's fine, after all it's okay to be wrong.

-Actually put in the time to improve VAC to stop cheaters from ruining not just this mode, but any mode they enter with speedhacks and what have you.

-Alter the Parish / Cold Stream finales on this mode specifically to start with bridge down / door open so Survivors at least have a chance to play.

-Synchronize Tank spawns for both teams. Either both teams get to block the path forward, or both teams have to chase the Survivors from the start of the level. This alone would fix one of the most infuriating issues with this mode.

-Allow AI Tanks to spawn if the team isn't full. Tanks are already weak enough in this mode with a pitiful 3,000 health, at least throw them a bone.

-Adding onto the previous point, give the Tanks a L4D1-esque speed boost if they're on fire in this mode. They're fragile enough as is, at the very least giving them the ability to potentially catch up at the cost of constantly losing health would be a fair trade-off.

tl;dr: Go play Riding My Survivor, it's the better "lol we're all the same infected" mutation, and it actually works properly. Better yet, just pick a good mutation like Bleed Out Versus or Follow The Liter.