The plumb bob would only give erroneous information whilst an external input is continuously applied, turning, accelerating, climbing or decending. Once that input is removed, the plumb bob would give accurate vertical information.
A sensible power setting, along with removal of inputs to the side stick/control column (not a natural response, I know) would soon indicate the correct recovery action required.
Loud rushing sound getting louder, pull up; very quiet or buffeting, push the nose down. Let go and follow the lead given by the lead weight to re-establish which way is up. Don't touch a thing until your ears have recovered.
It worked on gliders before I flew powered aircraft, along with a bit of wool on a stick in front of my nose. Admittedly it was in the airflow outside but the basic principle holds good.