Well, there's no doubt that it is impossible to treat Buddhism as a single, unified, and consistent phenomenon across the centuries and in various countries. So it is impossible to say "Buddhism is x" or "Buddhism is y" when speaking in broad general terms. What Buddhism is depends entirely on the
where, the
when, and even the
who being discussed. So while Japanese Buddhism is of course the Buddhism of people in Japan, it doesn't really require a great stretch of the imagination to consider that it is vastly different from the Buddhism of Gautama Buddha. I happen to share Dr. Katsumoto's opinion that Japanese Buddhism has very little to do with the teachings of Gautama Buddha. The Lotus Sutra was certainly composed long after his death and the contents are pretty much a thin foundation of Buddhism with a huge accretion of Brahman cosmological characters and all sorts of supernatural mumbo-jumbo nonsense....the very sort of thing that the
rationalistic foundation of early Buddhism was an active
rejection of. It is essentially what Buddhism looks like after a bunch of Hindus got through messing with it and a bunch of Chinese monks got through translating, mistranslating, editing out stuff, and just making up other stuff to insert. I can't imagine any way on earth Gautama Buddha would recognize either the Buddhism that arises from it or....more importantly....himself as presented in it. And Japanese Buddhism is very largely based on it. Especially as far as the laity are concerned, it is all about Kannon, Jizo, Fudo Myo-o, etc....none of which had anything whatsoever to do with what Gautama Buddha taught. You can't tell me that he would come to Japan and see all the zillions of Jizo statues....an earth god borrowed directly from Hinduism....and say, "Oh, yes. That's what I taught". Same for the great pantheon of gods, devas, etc. that the esoteric schools (
Shingon, primarily....founded by Kukai) have also imported from Hinduism.
Japanese Buddhism, especially as practiced by the laity, is by and large all about supernatural superstitions and characters. It is hardly distinguishable from theistic religions such as Christianity, with Kannon and Amida Buddha being pretty good analogs for Christ and Dainichi Nyorai being damned near an analog for God the Creator. One prays to them for intercession and salvation. I've yet to find where Gautama Buddha taught that salvation comes from outside one's own self or that I'm supposed to pray to
anybody at all. What started out as probably the only religion in the world teaching total personal responsibility for one's surroundings and eventual fate, without reliance upon any sort of
deus ex machina, by the time it reached Japan ended up being twisted around to almost entirely consisting of chanting/praying to various cosmic characters for personal salvation and divine intervention in everything from epidemics, natural disasters, and practically anything else that the theistic religions pray to their Creator about. No...Gautama wouldn't even begin to recognize Japanese Buddhism as being the end result of what he started. Interestingly, while revered, he is a rather minor character in Japanese Buddhism.
Have you read the Lotus Sutra? Are you aware that Shingon Buddhism holds that Kukai is
still alive?