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I think what is meant by "stroke mechanics" is efficiency. You can manipulate the ball in order to do more or less what you want and that is the "touch" but you are wasting time and energy doing it. It's the overall economy of motion which requires balance and good footwork.
Here is an example- Bojan has touch and some efficiency relative to amateurs but compared to ML he wastes a ton of energy, especially the way his left arm flails around. That extra motion throws off his balance and makes his strokes inconsistent. This means the more energy going managing his body than the less goes into the quality of the shot.
Off topic analogy-
It's like the difference between a ICE car and an electric car. An ICE only converts about ~30% of the energy generated from the combustion process into forward motion, the rest is wasted as heat vibration and noise. An electric motor has one moving part and converts ~90% of of the electrical energy into forward motion.
Very well explained, Players like Sharath Kamal, Quadri Aruna have similar problems. Once, the balance is lost, it gets worse with each stroke in the rally till the player who lost balance also loses the point.
Balance, economy and efficiency separates the 99.99% from the 0.01%
That's where all those hard years of training works the magic.