the problem with sturms is they are the starting unit (free unit) so it cant be to powerfull from the get go... thats why they were nerfed couple of times... and the combo with the kubel was too strong early on vs usf.
the solution would be to make the sturms better only if volks are going to be the starting unit so you would have to pay for them
you could make them the copy of pgrens in stats as well as the price of 340 mp (and to make it so they can be made only after one truck is set up so they dont come out to soon).
Think it had more to do with timing, like that terrible time Shocks were CP 1.
Also I'm pretty sure a PG-copy for the same price would be overperforming, since PGs can't build and repair. Wehrmacht players already say "PGs are good only for Schrecks" plenty enough.