I think what made it broken was the ability to call in a techless AI medium tank on top of having the Puma, more than the Puma itself, as this combo gave an endless supply of call-in AT and AI without ever needing to go past T1. I think in hindsight the wrong vehicle was nerfed and what should've gotten put into tech was the Command P4 rather than the Puma.
Although of course making the Puma a call-in or only require T2 would risk seeing MobDef nearly every game again because an easily available Puma simply fixes Ostheer's most glaring weakness.
+1
They could just both be made buildables, puma at t2 and command p4 at t3. That way you can't circumvent tech for either as it should be, and puma doesn't come at 11 minutes and be totally useless.