I do not understand why Soviet Mark Target needs to dissipate immediately when the plane is shot down. The planes get shot down almost immediately by OKW without any micro at all. That doesn't seem like a valid attempt at adding "counterplay" to the ability, that just makes it a waste of 80 muni. The plane will get shot down before the ability even starts in many cases, since a 5 second delay is being added.
As it starts immediately and can be activated on all units on the map in sight, it is a bit too strong in the current state of the game. The OKW base flaks are stupid, that's true (why not just remove the AA ability of them?).
But mark target staying active even on a tank not visible to your enemy is also a bit dumb. With mark target, T34/85 become kind of mini Tigers and currently there is nothing you can do about that. Mark Target itself is simply a stupid mechanic, as well as for OKWs Command Panther.