Raktenwerfer: pure defensive unit that needs to be crammed into a building to be useful. it is useful defensively
JP4: niche defensive unit. very powerful as a defensive unit especially with FSJ fausts but does not function at all on the offensive
Puma: to low in penetration to be useful late game. as you need to flank units with it but as the game progresses and more units are deployed in the field it becomes harder and harder to pull of and you rather use it like a m10 or jackson. it cannot do so however as at long it only penetrates the t-34 half of the time.
Volks : They are crap and only become a decent meatshield when they reach vet 5. while its much easier for them to get to vet 5 this is not a given.
You do realize that you just described Jackson issues in late game? Puma has same chances to penetrate Sherman like Jackson to penetrate vetted Panther (not to mention KT or JT). Not to mention that Puma has smoke to escape and great vet ability.