Right now all vehicles focus on hit point systems dating far back from 2001's Operation Flashpoint, and at the time the system composed of tracks, a gun and hull with several hits made it more advanced than most anything else.
Today however Arma has moved far beyond OFP in many things including ballistics, and while armor has gotten improvements such as ranging ballistics and thermals, it lacks greatly in the protection zone BUT also has far too much power in the situational awareness zone.
MBT's are less effective than they should be, why should I take a tank with a reload timer and far more limited ammo when I can take an APC? Why take either of those when I can use an AA vehicle to do the same?
As it stands the only difference between these two is that a tank can take 2 extra AT hits from the front and nothing else, it is slower and weaker by its lack of rapid fire.
Back in Operation Flashpoint, before running with AT's launchers, before standing or even walking with them..before leaning or corrective stances, armor was to be feared due to the limits of infantry..now however it is a big joke
So what can be done to improve this? Ultimately the only answer really is to make tanks more like the real thing, to have a MBT able to soak damage like a sponge without going up in flames..to drop HP (or mostly) in favor of modules), that a round from the back or side should really be what matters rather than "how many times can I hit it"
However a system such as this would make tanks greatly OP, with the ability to withstand many hits by using good tactics but to also see everything in a 360 arc is far too much...the player should NOT have a radar, without it they are blind and must rely on crew communication and input from outside sources. This means the tank can't see all threats instantly from any distance and always track them, which means that while infantry have to flank and hit the tank in the right spot...the tankers have to spot them first on their own.
With proper armor a tank would no longer need to cower before anti air batteries, the players would have a more difficult time deciding "MBT, APC or AAA?" and pick the right vehicle for the job rather than what spits out damage the quickest.