Interesting, Attila, that you chose to show us one of Hasui's pieces that depicts what is, to me at least, a very traditional scene from Japanese art. It was done very well by Utagawa Hiroshige, in his Tokkaido series (No 22, I think) of the Utsutani Pass. The same subject received the attention of Sotatsu and Roshu, before him.
I would have thought it was the perfect example of how different artists deal with a similar subject.
I think the assertion that there are different, distinct schools developing out of the one art, bonsai, is perhaps a little disingenuous. I see it more as a progression of fashions, not unlike fashions in men's clothing. The decorations and embellishments change but the basic shape remains the same. We are constrained to the needs of nature, though there is a gradual, cyclical evolution apparent. A little fuller now, a little tighter then but all recognisably linked, each to the other.
As with any fashion, be it clothes, art, music, literature, religion or anything else; there will always be a cadre of "traditionalists" who adhere to the tenets of what they consider to be the "true style". Bonsai is no different, in my view. It attracts people into "schools", and leaves them to their own devices, and to occasional scorn from the "progressives".
Tradition or no, there is little but opinion to determine whether one practitioner is right, or another wrong. (Admittedly, for someone to be "right" they usually feel compelled to make someone else "wrong"). However, if we are prepared to make the church broad enough then there is room for Walter and Andy to fit under the roof and respect each other's work from a distance, if not actively.
It is human nature to divide along tribal lines. Why should our art be any different?