I think that whats missing here is consideration of the fact that the USF can equip every infantry unit they have with a zook, or even double zooks. A 4-rifles blob firing 8 zooks every few seconds is bad enough as it is, and a dire threat to all axis armour.
Ost can't field nearly as many PG's, and OKW can only upgrade one shreck. This is quality versus quantity again and making zooks identical to shrecks would almost certainly destroy any parity between the two sides completely.
ETA: and making zooks cheaper would only make it even easier for USF to mass blob zooks.
A rifleblob all wielding zooks? Thats a problem? USF's AI squad meant to beat grens and volks all equipped with AI hindering weapons? Pull up your own infantry and watch the riflemen do little damage. "a dire threat to all Axis armor", as if, mate. Look at those posted stats again. Its not like USF has to deal with shrecks 100% penetrating nearly all their vehicles. Oh, wait...
And no one is asking for zooks asking to be identical to schreks. Shreks do 120 damage and their lowest pen is still better than a bazooka's highest pen. People want zooks to be better because they are still a crap investment overshadowed by many other things.
Eat a snickers.