I apologize for repeating myself, however, the question keeps repeating itself as well.
The Athenians said "We allow Alexander to call himself a god, if he wishes"
This hit on something that J.D. said, I believe, probably echoed by others ie: when Tai Chi, Hsing-I , Ba Gua and perhaps Ba Fa were initially touted as 'internal arts', it stuck. To some extent because it is at least partially true and, unlike Alexander, there is no discernible likelihood that these arts will die in the immediate future, thus disproving the proposition.
Also, to repeat myself, Sanchin claims and has positive health benefits from its practice. The Chinese Masters and/or those who write for them are inlikely to willingly admit this as they simply want to hang on to the label for themselves.
From their point of view this is sound business, and, from their perspective, truthful behaviour.
Their pride in what they feel a 'their' particular heritage may also be at stake.
Would you, if you were a Chines Master, say the following: "Oh yeah, that Japanese evolved Sanchin is a pretty good internal art too."
Maybe next year. Even if they did they would be at pains to point out, correctly,its roots.
Maybe some Chinese Masters or writers actually do admit it, but that will not equate to an admission that Sanchin might be as good as their internal arts.
Honestly, in some ways they would be right, and in some ways they would be wrong.