Not to mention that even without upgrades, American rifles overpower and outclass Ostheer Grenadiers. So where exactly do they begin to outscale American rifles? Or is my definition of scaling as number of options to approach any given situation not correct?
I think your definition of scaling is a bit off here, "scaling" is mainly referring to "evolution" (or rather quality of evolution) when applied to ingame units. Oberkommando Volksgrenadiere are a perfect example of scaling, even if they do nots have that much options/abilities (Shrecks are awesome, sure): they start being rather meh (durable, but meh), and scale very good in the lategame because of vet bonuses.
While if completely agree Wehrmacht has issues in 1v1 at the moment that should be resolved, i also think that Grenadiere scale very well : their LMG is very potent, and vet bonuses are enough to make them a solid all rounder at all stages of the game (i think they should be a reference point for balance of all infantry in the game).