Some of this is sound, some isn't.
Artillery should be powerful. It was the number one cause of death on the battlefield for a reason. Do not nerf it any further, it's already been nerfed considerably.
The day abandoned vehicles are removed is the day I stop playing and never return. RNG is not always a bad thing, abandonment is the absolute definition of RNG that enlivens the game. The only way it can be game changing is if you fail to destroy the vehicle yourself, and if you don't then it's your fault.
Not at all true. For example a 222 getting stolen nullifies any follow up light vehicle from Ostheer. Usually you are able to kill the decrewed tank, but not always, and that doesn't justify the other guy getting a free unit. As it is currently I wouldn't say you are forced to keep your vehicle with the bulk of your forces, but its definitely safer. If you send a medium or light vehicle to harass a capping squad on the side and they guy has a tank destroyer parked in the back, there is a 5% chance he gets a free unit even though you were using the unit the correct way.