I use 24 fret guitars.
And physics beyond the level of rudimentary and misunderstood - there is only a node at the location of 24th fret if you inhibit vibration there and force it to be a stationary point by touching your finger to it (or similar, pick, whatever). Otherwise, in an open string vibration your root mode (not node, mode) is nodal at the nut and bridge, anti-nodal at 12th and all other points are somewhere in between. This doesnt take into account overtones, of which there are likely hundreds in the vibration of a guitar string (and hes only taken into account 1 and recognised the existance of, what was it, 4?)
Antinodal points dont cancel 'mids', they cancel everything; they are points of ZERO vibration.
By his logic the bridge position would never have any mids because its right next to one of the only two points on a guitar string that are always nodal.
Also by his logic, there would be 'phase cancellation' (which he uses incorrectly; its physically impossible for any vibration or point of vibration on a bound harmonic oscilator to be out of phase with any other part, and this includes guitar strings) by shortening a string and playing on ANY fret. Same for playing different strings at the same time. Doesnt happen unless the guitars out of tune or badly intonated.
The laws of physics are absolute, he has them absolutely wrong, and is absolutely wrong.