I think you have a Tq indication problem, T4 and Ng are fine, Tq indication is low and requires calibration (30 minute job for 2 engines).
After 35 years working on the AS355 series myself, I have seen owners and engineers throw a lot of labour at the aircraft to get the engines balanced (as best as possible).
Always do your engine checks in flight iaw the flight manual, that is where you will be when you need full power on one engine if you have a problem.
1. Engine Tq calibration MUST be carried out and adjusted correctly (Intake airflow is different on each side in flight), if this is not done nothing will make sense. Remember we balance engines on Tq but adjust Ng.
2. Fly aircraft at 73% Tq and apply collective friction
3. Beep each engine in turn till you reach a TQ or T4 limitation, record figures
4. Adjust engine Ng on adjuster/ PTG arm angle / Beep trim actuator arm angle (on mgb decking) to ensure both engines are perfectly balanced
After this you will see if one engine is low power or not, I doubt it is, just needs a Tq calibration, ON BOTH ENGINES .
All pilots on this forum just love a well matched pair of engines on the AS355, not having to beep up or down every time he moves the collective makes flying so much nicer.
I have never failed to match engines on these aircraft unless their was a tired or faulty component