I think that only one sherck on SP is bad remember old PG with only 1 sherck blobing their way to base ,giving them 2 sherck remove their ai and 140 mun seems a fair price so 1 can't blob cause no ai and 2 can't have more than 2 squad cause you don't have infinite munitions
That way they become just slightly better pgrens. To keep them unique, I would give them one shreck + 3 mp40s at spawn and upgrade package that removes shreck but gives them 4 stgs, holdable sweeper and increased repair rate, for, lets say 60 muni. That way you cant blob double shrecked spios with stg volks till you win, one shreck on 340mp squad with weak AI is not enough to make blobbing worth it.