That video confused me. In my experience, moving from a 150 watts @ 8 ohm Wells Majestic integrated to a 250 watts @ 8 ohm Hegel H390 impacted more than the system’s ability to play loud.
In fact, when I first hooked up the Hegel, I was shocked, because my speakers sounded so much better. Unless one is restricting one’s choices to amps of varying power within the same product line of a single manufacturer, there will be differences between 10 amps of different brands with equal power ratings besides how loud/clean they play.
Perhaps I’m simply too ignorant re: the physics involved to grasp the value of the experiment in the video in terms of real world application.