Ground Vehicles have long had issues. Maybe they'll be fixed in AH2, maybe not.
The whole "I shot playerX Y times in the back from Z yards and then he turned around and killed me in one shot!" argument is strictly lag-based I think. What I think happens is some guy on a crap modem hops in a tank... trundles along, gets bushwhacked... You pop a round into him, you see a flash, you send a packet to HTC server saying "Hey, playerX just took a 75mm AP round to the rear"... HTC server sends to playerX... HTC server sends to player X.... HTC server sends to playerX... packet gets dropped. Rinse wash and repeat. He finally notices you, turns the turret around. HTC server sends your computer a packet saying "You just got hit in the head by a 75mm AP shell". Your computer says "Ok, thanks". You go boom.
I am absolutely convinced that dropping packets will render some GVs practically invulnerable as long as the guy has a crappy connection.
The shooting through walls thing is an incredibly old bug. You can shoot through buildings and hit vehicles behind them. Usually due to clipping issues you can SEE through buildings to know where to aim... thus all the "hacker" cries. It is a bug, people take advantage of it.
As far as "Player X hit me from 324526247625 yards with the first shot and killed me! Yea... some people ARE that good. It takes a lot of practice shooting the tank guns, but it is possible to land hits of 7k+ (or so I am given to understand, my max is probably about 4k). Adjust the sight upwards, fire a ranging shot.. see where it lands, then use the range bars appropriately. Plus if some tool is camping a ridge or a spawn... he has more than likely got that spot zeroed in. He knows exactly how far it is to you when you peek your little head over that ridge... so he knows how far to shoot to drop a shell on it.
As far as the damage modelling... yea, it is broken. It has been conclusively proven that the Panzer IV is far more vulnerable to strafing than it ever was in real life. The Tiger de-track epilepsy dance has been around since it was introduced. The M-8 is just worthless, as is the M-16.
But as has been said so many times over the years... this is a flight sim. Ground Vehicles were put in for fun. If you are a hyper-realism freak like me, you won't like the GVs. But most people don't care that in real life the Panzer IV was all but immune to Hizookas and .50s. They want to point their Spitfire at a tank and watch it blow up.