Since the hardener nerf, fighting tanks no longer feel like an overwhelming challenge. I can personally damage a tank enough with advanced swarms to make it retreat in fear, and with one or 2 more other AV players on the field we can manage to completely destroy a tank. In my opinion, this is how it should be. Sometimes I can even solo a militia tank if the driver is dumb enough to stick around. Tanks are much more expensive than AV, so I think its fair that solo-ing a tank should not be a common occurrence. I also don't think it that the price tag justifies taking an overwhelming force of AV to stop one tank like some tankers would like; while AV is much cheaper, it also requires teamwork, means less people on your team fulfilling objectives, and (with the exception of the commando) also it requires you to sacrifice the use of an anti-infantry light weapon. Anyway, I think where we are now is pretty close to the ideal.

There is still things that need to be fixed with vehicles:

Repair-tanking leads to near invincibility. I found this thread on the features and ideas board that shows how crazy it is. It basically means infantry don't ever have a realistic chance at destroying certain tanks and dropships. In one of the comments in the thread I link, one pilot shares a story of how it took clever coordination between 4 assault dropship pilots (including himself) to take down just one enemy assault dropship because of how obscenely effective repair tanking is.

Large blasters are still way too good at killing infantry. A giant plasma high ROF machinegun mounted on a tank to easily mow down infantry and rack up a ton of kills seems inherently overpowered, there is a thread on the subject here. I would prefer if large blaster turrets had 30% less ROF, but 30% more damage (hell I would fine with 35-40% more damage); the DPS would remain the same, but it wouldn't be so overly powerful against infantry. Do blasters really need as much range as they currently have? They can hit you further than swarm launchers can lock-on.

While this does not affect AV, at least not directly, railgun tanks should not out-DPS blaster tanks at close range. Their should be a tradeoff between range and DPS. You wouldn't give a sniper rifle more damage per second than an assault rifle, likewise you shouldn't give a large railgun turret higher DPS than a comparatively close range large blaster turret. At close range the large blasters should generally win, and at longer ranges the large railgun should have the advantage.

These are my thoughts on the issue, and balance seems fairly close.

In order to pull that off, some very big changes have to be made to the large blaster turret.

The best way I can think of to achieve this is a decrease in rate of fire, increase damage, drastic increase in spread, and having bullets randomly curve out like the forge guns of old. Essentially up the DPS but lower the accuracy to were its frustratingly annoying to kill smaller targets like infantry.