Greeb: Cons come "scaled" right out of the box, due to Oorah/Merge, 6man soak and cheaper reinforce. These remain eminent throughout the game.
Rest of scaling is handled as normal by veterancy, for which they have the same increases as Grens.
Grens and Volks are better at mid range.And Sturmpios' close range DPS are way better.
Oorah is the ability that balance conscripts, making up for their terrible damage output at long-mid ranges. Btw, they can't shoot while in Oorah.
Merge is not the OP ability you think. Reinforcing conscripts is not especially cheaper and effectively removes a conscript squad from the battle until reinforced.
You forgot to say that rifle and AT grenades come for free for Ost when teching, meanwhile soviet must spend fuel upgrading them. And both of them are inferior than the Ostheer ones.
About the squad size, 6 men squads can be an issue in support weapons, but is not always an advantage for infantry. Yes, it's more easy to wipe an axis squad with a nade, but in exchange, is barely impossible to keep a soviet squad in green cover. Reinforcing prices keeps them balanced.
Axis infantry also have their couple of useful abilities, like being able to heal themselves and much better vet bonuses.
In short, cons are perfectly balanced early game against grens. The thing is that grens can scale very well late game spending 60 ammo in a LMG upgrade, meanwhile cons doesn't scale at all. They don't get better abilities, or new weapons and even their vet bonuses are useless.
Cons are kept alive only for merging, stealing weapons or throwing ATnades.
Relic developers themselves had said plenty of times that conscripts are not mean to scale lategame, and they don't. Their uselfulness as a combat unit decreases very quickly, and from midgame onwards they have a role alike to the Combat Engineers, a unit with useful abilities but not able to fight against anything. Just to keep them at the back of the fighting forces and merge when required, and Oorah against any enemy vehicle and throw Atnades
(which against anything superior to a halftrack fails nearly always).
That is not scaling if their combat value is close to zero. They just remain useful, but not scaling at all.