Forget about G43 for a second. PFs are 270MP 0CP unit, from the get go they are weaker then volks at all ranges and have slightly better DPS at longer ranges, dont have access to sandbags. Lack of mid\close range DPS (which is not exeptional on volks aswell) means that your best bet with PFs is to camp in cover without moving much and hope that if enemy will somehow charge you, you will be able to hold your ground.
Volks on the other hand while not having super close\mid range DPS, they can still deliver a punch if charged badly, they can construct green cover and they can force enemy out of cover. In other words, in situations where volks have problems PFs have x2 problems + their own problems.
This is all about early. PFs arent underpowered\bad unit, but in early game they are intentionally handycapped because they will get G43s and G43 is so powerfull because they are rather weak early for the price. See the idea behind their balance?
In 1v1 and somewhat in 2v2 its a significant disadvantages, in 3v3 and 4v4 its not. And thats the reason why they are problem in big teamgames and lesser problem in smaller games. Because the core idea behind them is not working for every gamemode.
Seriously, stop exaggerating how weak they are to start the game. I understand you said that ELITE players can overcome PF weak opening yet you also said no one would ever go PF only. Zaney just posted a match between Isuldur and IncaUna and went full PF build which traded well EARLY with Rifles. Despite the fact that they cant build cover, have worse DPS and cost more he held similar map which he then used to leverage a Flaktrak so he could cover and start to upgrade his units.
We are in agreement that the unit composition in regards to DPS is the issue(G43 models) but the argument that they start weak so they need to be strong later makes no sense. How long are they "weak" is it until they get the G43 upgrades? Is it when they get Vet? The unit can usually start upgrading at 5-6 mins from start of game. Even games can go from 20-60 mins so it spends a fraction of its time being weak and most of the time overperforming. If it is with Vet, all they have to do is join the horde and earn some easy Vet.
By the way the game is a fairly good watch up until MID/Late game. I think it shows how bad Rifle company scales along with the Stuart which I think has to do with lack of decent indirect.