They're designed to be weak relative to Volks, which are units that start strong but scale badly.
I brought PF as an example of unit starting weak and become better than other units with time.
If you want to debate PF and the success of their implementation we can do so in an appropriate thread. Imo their use in the latest tournament is an indication that there are issues with them thou.
As for applying this to heavies, I think it'd exacarabate the problem. If a heavy needs to accumulate veterancy to be effective, players are going to deploy it as quickly as possible so it can do that before it's facing vetted tank destroyers.
Given heavies being rushed all the time is the entire problem, I don't think this'd help.
No the problem is not that heavies are rushed.
The original problem they tried to FIX was:
Tech skipping
Peromance in large MOD
Part of the current problem is their shock value and toning down the vet 0 performance would go along way in reducing the Super dominance. One would have to vet his super heavy before getting his weapon worth and that would make rushing them a bad investment the same way that one will find himself in very difficult spot if he decided to spam only PF.
In addition the idea that unit should be balanced based only on their vet 0 performance as suggested by exsile is problematic.