I stopped reading when you said volks are the best mainlines. Absolute hilarity.
Whenever I play ez mode v2.0 (OKW) my Volks always slaughter everyone elses mainlines except Tommies and Penals (if you consider Penals a mainline). Grens are really good too they might be now better actually.
The ranking for mainlines as far as over all effectiveness probably are:
1 - Grenadiers, barely take any damage, easy and cheap upgrades that outpreform BARs and Brens, hard counter to Conscripts and Rifleman
2 - Volksgrens, good upgrades with no side techs that come early which gives them an edge over opponents nullifying any advantages they would otherwise have
3 - Tommies used to be #1 before being beaten with the nerf hammer, weapon upgrades require a side tech despite their poor preformance, still okay vetted
4 - Cheap Soviet infantry with 6 men, not great combat wise but have decent upgrades with certain doctrines
5 - Riflemen stock preformance better than before, over all preformance very poor for 280 MP 28 reinforcement cost and 150 MP 15 fuel side tech and 120 munitions for double BARs just to keep up with Volksgren preformance, also no grenades without an additional side tech of 150 MP and 15 fuel, and no snare without vet 1. Perhaps the most hamstrung infantry unit in the game.