They are durable as rifles(not when vetted though, unless we talk ooc heal vs rec acc as both affect staying power).
They are packed with utility like cons(flame nades, possible doctrinal cancer nades, hard at, build sanbags).
They punch like grens(actually, they surpass grens unless grens go LMG).
They only lack cover acc bonus, other then that, they already have something from every other infantry squad, so they are pretty much like all the other infantry in one unit already.
And they definitely won't get weapon that wasn't used for years already.
That was some impressive mental gymnastics right there.
Let's not make them even more like 5 man grens/osttruppen with grenades by giving them the faust.
Also I am aware that the Panzerbuchse is outdated, I am not 100% on the idea. OKW has a problem with fighting early game light vehicle rushes until they get a few panzerschrecks out. The problem is the Panzerschrecks on all their mainline infantry are too effective a counter against late game armor, which OKW has plenty of tools to work with in the late game. There needs to be a solution that is good against stopping light vehicles, but meh against real armor. AT rifles perfectly fit this role. I don't see a better solution to the problem without relic having to add more content to the game, which they wont. The Panzerbuchse is already in the game in ToW.
I would also like to mention that I don't think volks are super OP with schrecks, but they are just a cancer for gameplay. It promotes poor play when your most effective anti-tank unit is also your effective infantry unit. The weight of OKW AT needs to be shifted onto their other units instead of the volks.