Why don't you link the popcap to the territory hold? Just make sure it isn't possible at all to only hold 1/3 of the map and still be able to call-in super heavy.
All those issues are link to that "easy" popcap and upkeep design. And was mitigated in vCoh.
There are some other ways to limit call-in link having a Victory point cost per call-in unit, make Tiger/ISU costing 100 victory points and you'll definitively see less of them in hands of bad players. You can also do the same with E8 and all other med-tanks with a cost of 50 victory points per tank and all other freaky small units like falls/vetted rifles etc.. + dodge and mech troop cost 3,5 or 10 points.
In fact I don't care, the only unit I call-in is the dodge

for the rest I'm 100% with you, call-in meta is an issue.
Edit:
Coming back to popcap, you can link the call-in to territory hold. It was use in Sudden Strike game. You must hold 2 victory point for 10 or 15 minutes (not in a raw) to be able to call-in med tanks and 25 minutes to call-in Super Heavy.
In fact, CP aren't really working today cause they were design for vCoh meta, which isn't anymore the same than Coh2, so it need to be changed to something that has a cooldown or a timer linked to the game victory process, not anymore a timer independent of it like are CPs.