That's the worst excuse ever!
Grens need less to fully reinforce only when they can die less frequently than other Core infantry
In fact no, Grens aren't more versatile than Volks, Rifles or Tommies..
They will suffer casualty in first salvo of changing fire
Considering that there are less grenadiers on the field in the first place, they are certainly going to die a lot less than their opponent on average. (The losing player tends to bleed more manpower reinforcing. That's why they are losing.)
The LMG upgrade lets grenadiers burst down models really fast too you know. Having all that DPS concentrated on one guy also means that taking losses in a fight isn't as big of a deal as it is with allied infantry.
You guys are so focused on "Waaah Grenadiers aren't as good as Riflemen, why are they more expensive to reinforce" you're ignoring how their reinforcement cost fits into their role in the game and the rest of their faction. The Ostheer economy is very different from the American one or the Brit one.