In my experience increasing the magnification beyond the point where full detail is seen is of considerable benefit.
It makes the detection of hidden detail more likely.
Just barely using the minimum full detail magnification does give a brighter image, but does not reveal all there is to be seen.
With a test chart, one knows what is there.
This is an entirely different observation to detecting hidden unknown detail.
This is from my observations as a planetary observer.
With my 317mm Dall Kirkham my normal magnification was 265x.
But this was increased to 400x to detect the fine detail.
It was only beyond 700x that I would call it empty magnification.
Of course with fine Seeing. But the scope could not show more above 700x.
Paul Doherty, who could see Jupiter's moons without optical aid, used 190x on his 305mm Newtonian.
Probably more for fine detail.
So someone with exceptional sight needs less magnification and sees more because of the brighter image.
In short, I would not use the term 'Empty magnification' at just beyond the minimum magnification needed to see all the detail, but at considerably higher magnifications.
Also empty magnification applies in my opinion to the quality of the telescope.
With the Pentax 100mm f/12 refractor 300x was certainly not empty magnification.
Rev Dawes used over 400x on his fine 6.5 inch approx. refractor on Jupiter, Jupiter's moons, and Mars in his published drawings.
He would not have called this empty magnification.
With the Harpia it seems to be that the quality of the optics is not great, especially if above 70x is considered empty magnification.
I would expect to be able to use 200x with a 93mm aperture Harpia if it was any good.