You can't understand why someone would like their own baseline infantry unit that can compete with enemy baseline infantry?
Does your mom tie your shoes in the morning or do you have velcro?
Play US then.
Guards are your LMG Grenadiers and Shocks are your Assault grenadiers but better.
Changing Soviets to have core infantry unit that scales into late game would require complete faction re design.
Giving PPSH as a non doctrinal upgrade or doing something to Conscripts will tweak balance completely in Soviet favor and brake it completely.
You need to think about bigger picture than your own wishes and hopes.