5 man rifle squad with all CQC weapons and nothing to close the gap (except a HT that can be 2 shotted easily) would fall apart late game. The reason Thompson Para's work is they are 6 men and have much better veterancy, also they have a special ability that is pure rape.
CQC focused squad + late game + no ability to close = ded.
Again, I said mediocre. They wouldn't be bad by any stretch of the imagination but they would just compound the added drain issues USF has.
*Cough, they have a shock-style smoke grenade and a regular grenade cough*
Also, no reason to change change their abilities ad vet to that of base rifles.