I think a lot of folks (or Volks? Lol) give the Germans too much credit for having only the best equipment. AT rifles were used during the later part of the war by the Germans for the same reasons they used other older equipment alongside their other, newer and better, equipment: because they didn’t have enough of the good stuff.
It is totally reasonable to see AT rifles in the hands of German infantry units from 1939 all the way to 1945 because they never produced enough replacement equipment to meet the needs of their operational forces in the field. Even the US fielded M1903 Springfield bolt action rifles in some numbers in units fighting in Italy in 1945 (and not as sniper rifles, I mean as regular infantry rifles), and it is without a doubt that the US was in the best position in terms of production of war material when compared to anyone else at the time.
TL, DR: AT rifles are fine historically for the Germans to use and I do like this proposal to give a little bit of flexibility to the Ostheer, who do struggle vs light vehicles.
AT rifles were probably still being used, yes. But specifically NOT the Pzb39, which were almost entirely converted into dedicated grenade launchers.
It should also be noted this rifle had far worse anti-armor and anti-material capability than the PTRS it is being compared to, which severely limits the realistic capability of this package to be used against the T-70s, SU-76Ms, M5 Stuarts, and AECs that would seem to necessitate it (all other light vehicles the 222 is perfectly capable of countering)
On a further historical note, the Springfield was still seeing mass deployment mostly because it was the most reliable and effective platform for the firing of rifle grenades; the M7 system for the M1 Garand was never fully deployed before the Normandy landings and the Springfield (M1 grenade launcher device) and even M1 carbine (M8 grenade launcher device) were considered more reliable platforms for firing rifle grenades. For a good part of the war the grenadier in the US Army rifle squad was equipped with a Springfield bolt-action rifle.
(The Pzb39 was also a single shot weapon, but lelic seems to have forgotten about this)