On second look I think reserve army actually pushes a really unique play style that no other commander really supports. T1 + Conscripts or mixing Penals and Conscripts might not be incredibly strong but it is a very unique play style that the commander pushes. I think it doesn’t need a rework but could benefit from exchanging the ML20 for something else. The artillery doesn’t fit the best in this infantry based doctrine and doesn’t contribute much to the commander unless your just looming for artillery in team games. Some sort of late game call in like an artillery strike, a buff like for the motherland, or even maybe something crazy like the IS2 could probably be a good improvement to the doctrine and make sure this unique play style has the best chance to see some use.
I too think reserve army would be a very decent commander with a Is2 instead of the ml20 and I'm sure loads of people would love a third is2 commander.
On the other hand the new ml20 is also better and more focus for supporting infantry and I don't want to dwindle the ml20 any further.