The issue is with understanding - things like strategy, the principles behind the movements, etc. Those concepts must be dealt with in the mind of the student, and that mind is where the differences occur.
In VT the strategy which requires understanding by the mind is very sparse, and it is recorded quite explicitly in writing.
As Philipp Bayer says, "Understanding the genius of Ving Tsun should not take longer than an afternoon. By then, everything should be clear"
Understanding of strategy and tactic is indeed passed into the body and mind via physical exercises, not by listening to the teacher speak. Learning the system physically in the correct way is by far the most important thing.
As for the art being transmitted entirely physically, that's perception.
No, it isn't. System understanding is required by the teacher. It isn't required by the student. Knowing the reason for performing a particular drill is of course very useful in terms of understanding, but the system is not learned by listening, pondering, coming up with ideas and new developments. Provided practice is taken seriously and training is done to the best of one's abilities, VT can be learned fully while having only very basic conscious conceptual understanding of the system.
What it does require though is immense trust and perseverence.
You've already discussed the fact that YM was sparing in his dissemination of information, not sharing the same explanations with every student, but still presented the entirety of the physical movement in a logical, step-by-step order.
YM certainly didn't share the entirety of the physical movement with every student. Many simply copied other students. Many did not complete the system. Many never fought with VT for example, which is a necessary part of the development.
Where YM did show teach the physical movements to particular individuals (of course in the correct order, at the correct time), what he often didn't do was make sure the students knew what they were doing. Many therefore left with parts of the system, not yet functional, which they assumed were for other things than the actual purpose, for example chi sau drills. Many also created their own understanding of why they were doing certain exercises, which quickly led to the degeneration of their wing chun.
By looking at some of the wing chun derived from YM's teaching it is often clearly possible to tell where the originator of the style stopped learning the system from YM.