This YouTuber assumes everyone wants their mini's to be painted to a higher level of detail. That is an errant assumption.
I hate overly detailed mini's -- I will never paint excessive details. I view my mini's at arm's length, or even further away, 99% of the time. For that reason, I paint for the 99% of my viewing time, not the 1%. 'Thick paint showing brush strokes'? Maybe, but I can't see them when my mini's are on the tabletop, so I really do not care if brush strokes exist, or not. The 99% is all I care about. The excessive details, even when painted, are not visible at 3+ feet distance, on my 20mm-28mm figures, for my eyes. If I cannot see them, they do not exist -- and I will not paint them. ;-)
Thinning paint may avoid covering finely sculpted details, but it also adds considerable painting time! Thin paint requires multiple coats to achieve coverage. I am an army painter, I am a speed painter. Thinning paint would slow me down to a fraction of my output.
A friend paints very good eyes on 15mm figures! On the tabletop, I only saw some of his mini's as formless green blobs. When I picked them up, holding them 3 inches from my eye, I saw remarkable paint work on them, including white eyes, with dark pupils, which were skillfully done, indeed… Again, on the tabletop, they appeared to be small green blobs. My vision is 20/20 with eyeglasses. They were just so small, that on the tabletop, they were indeterminate as to race, being shapeless forms. His answer when I questioned him why he painted to such a detailed level, when it could not be seen more than 3 inches from the eye? "I would know if they were not painted to such a high level." His issue, not mine, I assure you.
If everyone in the world painted for the details which can only be observed holding the mini's three inches from their eyeball, I would still paint for my 99%. The premise that everyone wants to paint to a high level of detail, is false.
Everyone on YouTube assumes that everyone on planet Earth wants to paint like them, to an excruciating level of detail… Sorry. Simply not true. All I paint for, is figures that look decent at 3+ feet! After that, I don't care. Happily swimming against the current, for nearly three decades. Cheers!