Reduce costs to get to T4, increase costs of teching for USF and OKW.
Units themselves are mostly fine, but relic slowed down teching for vanila armies for a reason and that reason certainly wasn't so we could get new armies with ultra fast teching.
Old armies need to invest a hefty amount of time, menpower and fuel on their teching, new armies do not even notice any strain on the resources when teching not to mention the time saved because of no need to retreat builder unit and use it to get the tier building up and runnig. That is the problem here.
I suspect you are right in that units probably are reaonably balanced and I agree time to tech and costs to tech are problematic. They result in, when I'm playing wehr, always having fewer tanks in the field than the enemy up until a late game so late most matches have already concluded. Tanks become support vehicles or part of combined arms push by necessity because if they operate by themselves they will get outnumbered and outgunned.