This is blatantly incorrect considering that you play Ostruppen and Grens completely differently due to their toolsets. Just because both units come out of Infantry Company now doesn't mean they are the same unit. That's akin to calling Conscripts and Grens the same unit which is an absurd notion.
Let me see now:
Grenadiers are a defensive infatry with a faust, that comes from t1 and can upgrade with an LMG
Ostruppen are a defensive infatry with a faust, that comes from t1 and can upgrade with an LMG
Yes that sound completely different game play.
(although irrelevant Conscripts are T0 not T1)
The nerfs to Ostruppen were perfectly warranted because they were batshit insanely efficient in the hands of someone capable meaning you simply couldn't overcome their raw speed and effectiveness to cost ratio. Slowing them down was as a necessity without losing the spirit of the unit.
Only problem with that theory was that the original spirit of the unit was "raw speed and effectiveness to cost ratio" and the unit has almost lost its spirit.