This again..
How many times do we have to do the inane vehicle nerf dance?
Fix the resource system. Hell, make vehicles cost certs to unlock too while you're at it (and just give people who've already spent a couple of thousand certs on a vehicle the unlock automatically).
Seriously, the problem isn't that vehicles can instagib infantry - it's a giant hulk of metal that fires out exploding shells the size of someone's leg, what do you expect to happen if that hits you? - the problem is the limiting factors already in the game, that should logically work to limit vehicle numbers, are broken.