They were never meant to trade efficiently late game, hence they don't. Obers or one of multiple different doctrinal infantry were always supposed to be supplement to volks. Only times when volks were self reliant were when they were op.
Volks have to draw fire/tie down enemy inf as they where designed to do. Then let obers or whatever elite callin inf is out their deals the damage. Although the only thing that i would change on volks is their self heal to vet 3 and buff recc acc a bit at vet 5.
Accualy beating/bleeding inf isent the job for volks late game. Its obers wich should be made viable for this.
If we buff volks to section rifle level obers become irrelevant and faction play more simaler across the board. Wich imo isent good.
Volksgrenadiers are absolutely lost and hopeless against 7 men cons, the role you decided to attribute them is irrelevant, they are priced for better performances