@CONSO:
The jackscrew (moving the entire horizontal stabilizer) makes slow / large changes of pitch moment, essentially for trim.
The hydraulically actuated elevator surfaces make fast / smaller changes of pitch moment for control of airspeed and flight path.
Jet transports have very broad CG limits. They can also experience changes of pitch moments with airspeed variation (mach number effects) and flap operation. For these reasons, they need the gigantic pitch authority provided by the movable HS.