You'll have to name them.
- Volks were way cheaper (235MP and 5 popcap) and had way better RA (with vet) and better vet in general than Panzerfusiliers;
- Volks back then had no other upgrades and there was nothing else in stock OKW roster to spend munitions on (except Obers);
- Back then Volks got crazy amounts of experience from hitting vehicles which allowed them to vet up really fast, further increasing their remaining AI. That's no longer the case;
- There were no other strategic choices, unlike now where one must choose between AI or AT upgrades;
- Panzerfusiliers with 2x Schrecks have practically no AI DPS left, unlike Volks Schrecks that still had pretty decent AI. One Allied stock mainline infantry squad has a good chance at fighting off up to three Panzerschreck Panzerfusiliers squads, an upgraded squad will do so with ease;
- Back then, Panzerschrecks had a decent chance to snipe an infantry model (especially with all the accuracy bonusses Volks got from vet back then), further increasing Schrecked Volks' AI power. Now Panzerschrecks have been adjusted to deal barely any damage to infantry at all (30 damage on a direct hit, which is unlikely because of a 0.5 accuracy modifier versus infantry);
- Panzerfusiliers are super munitions heavy with 90 MU and 120 MU upgrades;
- The doctrine itself is pretty munitions heavy.
You need 2 squads to ensure a wipe on 90% of tanks Allied can field or to force instant retreat for those medium.
Panzerschrecks deal 120 damage per shot. Assuming all four shots connect, which is unlikely at longer ranges, it will do a maximum of 480 alpha damage which is 160 damage short of killing a medium tank (640 HP). You need 6 shots to kill one so either you'd need three squads (840 manpower and 360 munitions) and very good RNG or you need to get follow up shots.
If we're just looking at forcing off tanks, two Panzerfusiliers with Panzerschrecks cost more than two Royal Engineers with 4x PIATs which is also enough to force off any Axis medium tank, so I don't really see how that's an argument. It's their job to force off tanks, that's why you'd bring infantry to counter them. And unlike the old Schrecked Volksgrenadiers, Schrecked Panzerfusiliers don't stand a chance against enemy infantry. Their AI is so poor they lose to Rear Echelon Troops.
I'm not saying Panzerfusilier Panzerschreck blobs are not a concern. That's why both the passive vet and the doctrinal sprint will likely be replaced preemptively. But I do think most people are overestimating their effectiveness, especially because comparing them to the old Volksgrenadiers is wrong.