Weapon stats can be adjusted to make anything useful.
Additionally, one Thompson per USF Captain and Lieutenant isn’t useless just because it’s the only SMG in the squad. A single MP40 would give the Grenadier squad firepower up close to repel an enemy assault as long as the 4 K98s in the squad can reduce the attackers as they close.
So no, for many reasons an MP40 wouldn’t be useless, it just wouldn’t be a powerhouse assault unit.
And since weapon stats are easily modified, for this implementation an MP40 or StG44 could have the EXACT SAME stats. So the choice between them is mostly a question of which you prefer aesthetically or historically.
rifleman is mid-short range combat unit and grenadier is long range combat unit
thompson in rifle squad and mp40 in grenadier squad is different
1 mp40 cant be effective in close range