Not Mike, but I'll offer a thought. The brush is basically an extension of your arm. In the hands of an expert, the brush is an extension of their mind and body. Watching an "expert" brush a character, a trained person can discern how much arm or mind/body connection is involved.
From there, the trained person could also gauge how good the "expert" might be at wielding a sword, because the principles of body usage are the same.
It's the same reasoning Ueshiba gave some dancer a 10th dan in Aikido after merely watching a performance.
Hi Ignatius - Thanks. I definitely hear you. I was meaning like ... maybe a specific thing along the lines you discuss in general. Maybe it's an impossible question over the intertube.