But one thing for folks to remember is that Buddhism did change and evolve over many centuries, as it passed from culture to culture in Asia. The Buddha lived 2500 years ago in ancient India, whereupon the philosophy passed to China 1000 years later, and then to someone like Master Dogen who lived about 1000 years after that in medieval Japan. You and I live in the strange world known as the 21st century. Certainly, some changes arose along the way in some important interpretations and outer forms. For example, the Chinese made Zen Practice very Chinese, the Japanese very medieval Japanese, and now we are making it very Western.
However, the Heart of the Buddha's teachings ... the Four Noble Truths, the Eightfold Path, Non-Self, Non-Attachment, the Middle Way, etc. etc., ... All are here now as much as there then!!
On the one hand some outer stuff is, well, changed. For example, when Buddhism came to China it was heavily influenced by, and pretty much merged with, Taoism (not to mention that it was already "Mahayana Buddhism" by that time, a very different flavor from the original). The result was this little thing we now call "Zen Buddhism". So, congratulations, we are already "Taoists" and "Mahayana Buddhists" ... not just "Buddhists". When it got to Japan, the Japanese added Japanese culture to it such as emphasis on proper "form" and decorum. In the West, we are now making some very good changes (although we have to, of course, try to avoid bad changes). These good changes include equality of the sexes and a greater emphasis on lay practice.
But it is still Buddhism. What Dogen taught was Buddhism. What we do around Treeleaf (I do believe) is as Buddhism as Buddhism can be.
I will even go so far as to say (and this is the kind of statement that has gotten me into all kinds of trouble on with some folks in Buddhism's own fundamentalist quarters) that maybe, just maybe, later Buddhism actually made some big and important "improvements" to the Buddha's original formulation with all those additions, and a couple of thousand years of working out the kinks and bugs. It is much like saying that Buddha was Henry Ford, who first thought up the brilliant idea of sticking 4 wheels on an internal combustion engine, but now we can drive a Prius! I even say that maybe, just maybe, the Buddha was not infallible on every darn thing and, while he was 90% right in his proposals, he also had some klunkers and narrow ideas here and there (as fits a man who lived in a traditional, myth based society some 2500 years ago in ancient India) ... like the whole thing about an overly mechanical view of rebirth, the place of women, the need to abandon the world and family in order to Practice and to repress or extinquish (as opposed to moderate & balance & pierce) the desires and emotions. ...
Also, do not forget that what the Buddha taught was an oral tradition for hundreds of years, passed down orally alone, until somebody finally wrote it all down hundreds of years after he was dead ... and then all the Buddhists immediately set to disagreeing about which of them had the "authentic" teachings. (The book "What the Buddha Taught" tries to play down that fact). That is why a study of the entire history of Buddhism is useful in knowing the interpretation(s) of the "Eightfold Path".
Dogen was different from Shakyamuni Buddha, who are both different from all of us.
But when we are sitting a moment of Zazen ... perfectly whole, just complete unto itself, without borders and duration, not long or short, nothing to add or take away, containing all moments and no moments in "this one moment" ... piercing Dukkha, attaining non-self, non-attached ... then there is not the slightest gap between each of us and the Buddha.