people need to understand that not every game, people use HTD/PPSH doctrine.
conscripts need lower reinforcement costs and a late game upgun option. im actually in favor of a SVT-40 package upgrade from HQ when T3 or T4 is up. this is to help them be more effective late game against german infantry.
reasons as explained, conscripts are fine early game, but have no place late game especially without HTD/PPSH upgrade as they do not output enough dps to stop panzergrens from rolling a bunch of them.
2ndly, they lose alot of models due to the fact of 1 armour value. this alone should justify the reduction in reinforcement costs.
in comparison, grenadiers scale well into late game with LMG42. although its unlocked early in the game, only stupid german players will get it early in the game, its a mid game option against infantry swarms and especially lethal on vetted grenadiers. they have a better armor value = more survivability. they comes in a 4 man squad, lowering AOE damage and reducing chances of squad AI bunching up.
honestly grenadiers are great at where they are now, they are the best generalist infantry in the game. place them in cover and firing, they will outdo anyone less than a shocktrooper and of course, they mustnt get hit by nades and yes they are great against guards in cover.
They're still usable through merging (a powerful ability economics-wise), capping, AT nading and flanking weaker enemies (PAKs, any Mg still alive, Panzerwerfers, ect.). Grenadier's fausts in comparison become worthless because the battlefield becomes way too lethal, and as you say they can only stand in cover and shoot since they lack the Hussein Bolt button that makes conscripts so good and versatile. Provided the Soviet hasn't yet fielded the myriads of units that can stop such things dead in their track (T70s, SU-76s, Katyushas, snipers especially if vetted, T-34s, Shock Troops all handily counter grens). I rarely have even vetted grens be useful late-game; they're just too fragile. Like Conscripts, they fall out hard but have less utility to fall back on. Basic infantry becoming less powerful late game is completely normal and is definitely not unique to conscripts. At least PPShs and HtD scales well into the late-game; the only German equivalent, G43s, is barely an upgrade over the LMG, and is arguably a downgrade for PGrens.
I also find Guards with DP-28s will beat grens, and even PGrens sometimes. Soviet has access to elite infantry that's superior to the German's, so it seems normal that conscripts fall off more if they aren't upgraded. In VCOH Volks fell out far more than Rifles (assuming veterancy on both sides), but that was compensated by Grenadiers being very powerful with vet.
Now, I agree that doctrines that give no elite infantry for Soviets do suck. But that's a larger balance issue; half the doctrines in the game are near-worthless if you ask me anyway.