The purpose of creating vehicle maps is not to make World of Tanks. You still have infantry. It is the map, game mode and the objectives themselves that cater to vehicles, rather than re-enacting the battle of Kursk (I‘m sure there is a tank battle somewhere on a planet called Kursk in the 40K universe). But it‘s still EC, and you can still exit vehicles.
Regarding balance of the various vehicles, I‘ve seen the prototype vehicle customization system in action, wherein we can now create new visual prefabs you can get and spawn into. It‘s not like fitting your character.;you choose prefabs. Then we‘ll one day be able to have variations (i.e., Predator vs. Baal Predator) which of course would get a balancing pass.