pioneers are ok. they're not very good but neither are RETs or ngies.
Pioneers (200MP) cost more than RET's (160) and Engineers (170) but have less range and utility. RET's can Volley Fire and Engineers can construct Demo Charges. They do more damage up close, but have a faster fall-off than all other SMG units, even weapon crews.
While RET's and Engineers can be used as supporting units in cover against enemy infantry, Pioneers must close in out of cover. They are also virtually useless against USF because Riflemen tear them down and RET's pin them with Volley Fire.
Compared to their current weapons, Pioneers would be better off with Volk or Fusilier rifles over their current MP 40's. That's why I think they deserve a slight buff. Alternatively, they could just be reduced to 170 MP like Combat Engineers.