No it is. Both volks and grens just require 60 muni nothing more to peak. Cons require additional fuel mp and 50 muni to peak and their peak comes later.
You know just because OST and OKW don't have a choice of getting their weapons early that doesn't mean it shouldn't counted as investment.
It's only 15 fuel in fact most of the allies side tech(what you call investment) is super cheap.
The reason why you have to spend fuel to get snares is because non of the allied faction need to build tech to get mainlines.
OST/OKW can't get just spend 15 fuel and get LMG's/stgs or rifle nades/incendiary nades but USF and UKF can.
Just because allied factions have the choice and ost/okw don't doesn't mean that ost and okw for infantry.
And before you say you tech up also with those i'll say allied tech is less expensive. OST can't even reach the final tech level before every other faction can.