Grenadier being 4 men is part of their identity. As someone who've played coh1 since release, a 5 men grenadier wouldn't feel right.
However... CoH2 grens are not exactly the same as CoH1 grens. Because in CoH1, the T1 infantry unit was volks, and Grens were a T2 unit. Moreover, the relationship between both German units and their opposition is quite different in CoH2.
First and foremost, there is a huge difference in the survivability of the Axis squads. In CoH1, a US Rifle squad had 6 men with 55HP each, for a total of 330HP in the sqaud.
Up against this went a Volksgren squad, with 5 models, at 60HP each, for a total of 300HP in the squad. And of course the Gren squad, with 80HP each, for a total of 320HP.
So in CoH1, each squad had a similar amount of HP, even if the number of models differed. 300, 320, 330. But this is not the case in CoH2; all basic infantry have the same 80HP. Which means that a Conscript squad has 480HP, a Rifles squad has 400HP, and a Grens squad has 320HP.
This change is especially notable when it comes to explosions and AOE attacks. The fact was that in CoH1 it took a lot more damage to kill a gren, and even a volksgren, than to kill a rifleman. So even when they were being bombed and shelled and mortared, they could not only take damage and remain combat effective for longer, but they were much less likely to suffer a wipe. And then if they did get wipe, because of the veterancy system they had, it didn't matter as much.
CoH2 grens are much, much weaker than their CoH1 counterparts. And that's maybe possibly OK, now that they are T1 units. On the other hand, Wehr no longer has a T2 line infantry unit, only the very expensive PG's who are medium ranged, don't have access to LMG42, and are just as squishy.
And Wehr also no longer has the more survivable Volks to screen the grens, cap points, etc.
CoH2 grens are really quite different to CoH1 grens, and I don't think nostalgia is a sufficient reason to keep them as they are. CoH1 kept that main infantry units roughly similar to each other, but in CoH2, the smaller squads really are much weaker. The grenade that in CoH1 would have killed a few grens, but left the squad unwiped, is now much more likely to wipe.
It isn't really surprising then that we so often see Wehr late game dominated by vehicles, with only a scattering of surviving infantry. And at that point, building more grens in the face of BAR'd up rifles and Shocks and whatnot is probably a losing proposition. The relative weakness of CoH2 grens is not a matter of perception or Axis fandom.
Personally, at this point, I think upgrading grens to a 5-model squad is a reasonable thing to suggest. It still won't make them as survivable as their CoH1 cousins, but it will at least make them more viable and reliable than they are at present.