@MADMAC50KThe 1 AP grenade nerf was quickly reverted, yes, there are 2 now.
Even in the worst case scenario, you can launch a rocket and then follow up with an underbarrel AP faster than most vehicles can pop APS, and deal around half their health in damage that way. And a ground vehicle can't always reach you like a helicopter can. If they have APS, half the time you will have a decent opportunity to take cover. To be honest, the APS is very bugged, it destroys projectiles right next to the vehicle unlike what its description says, the light is often broken, being nonexistent or red when the APS is on, or green or yellow (red and green at the same time???) when off. That's still not completely gamebreaking.
They're not helicopters, they won't fly away where no one can reach them and have full health, they'll still be in the general area, still at half health. If you die, you can respawn and hunt the vehicle down unless it completely retreated into their spawn (which is a different issue), or it retreated deep into their non-spawn territory (which I think is fine, and does not completely stop you). Or, you can have teammates. For the RAM or Brawler specifically, you can poke them with the NTW-50 which deals pretty substantial damage (14 to Brawler, I believe 18 to RAM but depends on direction a lot?), is unaffected by APS and can be used from farther away.
I think in the general engineer case having to limit your weapon selection and sometimes but not always dying 1-3* times to still get the vehicle kill solo (which often nets 2-4 player kills) if there is no decent teammate around is fine. And if there is a teammate around, no AP UGLs are needed, RPGs are strong by themselves. Again, not like air vehicles with 1-2 players in them, where 10 people with stingers spread around the whole map won't kill the attack heli that flew outside the map any faster.
*Probably bad spawns