So whats the point locking it behind teching?
The tank cannot fight with other tanks. No one will pull a command panzer as their first vehicle. In practice you choose T3 or T4, build a normal tank, THEN call in a P4 to receive aura boost.
all i am suggest is really give it a build time. for me i think all call in should have a build time. like I really dislike the idea when you destroy a heavy call in tank, as long as they have resource, they can immediate get another one. which give you no real window to advance or benefit to focus fire on destroy the heavy tank, might as well kill more infantry give him more MP bleed.