Thats debatable. A lot of people would still save to spend fuel on the heavy call-ins and requiring a building doesn't change that. They should be limited to one at a time (at least the better ones) and have zero fuel cost, that way they support the units you choose to make in game rather than being your main armor force.
It does change as it reduces the call-in spam, right now you can't save up 400 fuel and just wait for the cps, this change requires to spend that fuel for teching thus there won't be as many call-ins as we have in the live version atm.
But you are right...limiting them would be the best option, but having zero fuel cost is a bit too harsh imo...just look at the TA. It's possible to call it in at anytime because of the zero fuel cost, I had many games where I just pumped out vetted troops and had many armor, dugged in...saved up 800 mp and GG.