Very good video, as he provided verifiable evidence of the differences (Unlike some posters in forums), however this has been known since the first amps were produced.
He forgot mention the power supply and output stage which also plays a big part in how the amp can drive the speakers, as if the amp cannot provide enough current for lower impedance loads the sound will change.
This has been known for decades and easily measurable so fully verified, after having said that if driving a pure resistive 8 ohm load then differences will be small (Frequency response, distortion variations etc.) so those that say say amps are all the same are correct, but in the real world it is not just black and white.
Bill