For me the ultimate test of technique is easiness. When something becomes easy, then the technique to accomplish it has been mastered.
I think he was saying this in mechanical vs. fluidity.
Mechanical school of thought is to hyperfocus on convoluted fingering technique that is not memorable to the unconscious.
Sort of like forcing yourself to walk unnaturally.
It never becomes easy because it never integrates. You’re not taking the path of least resistance, you’re intentionally increasing resistance in your technique.
Bernhard, I think, was saying that practicing via these overly-mechanical schools means you never master the piece.
Pianists like Chopin and Liszt ended up culling out the hyperfocused mechanics and as a result could play pieces with unconventional technique (at-the-time) and learn them in such a way that they could recall them after years of not playing them.
Overly mechanical techniques will be forgotten until you relearn to play the convoluted way.