They are not talking about the members' personal lives or history. This is not that kind of documentary, it would have been only released on DVD then and no need to put it in the movie theatres because nobody would watch except hardcore fans, if you go into details of the lives of 7 unknown Japanese guys... It would have been pretty boring to regular moviegoers or film festival audiences - and this movie was clearly aimed at keeping moviegoers in their seats.
It's more like a dramatic movie, centered around Yoshiki and the various losses he experienced, hide's death, Toshi's departure and how the band came back together. There is nothing about Pata or Heath or Taiji's childhood or anything like that. They give short interviews in the movie, like, really short. Kijak said that they were pretty reclusive (Pata and Heath) and they didnt want to go for the very formal Japanese interpretation. The DVD has extra interviews with the members included.
The film itself is rather visual, and very much dramatic, slated to invoke sympathy and curiosity from viewers. I don't think you will learn a lot from it if you are a long time fan. There are some bts scenes of the Madison Square Garden concert and they visit hide and Taiji's gravesite. Other musicians and celebrities talk about X and Yoshiki (Marilyn Manson, Stan Lee, Richard Fortus, Gene Simmons, Sir George Martin). There's color footage of hide's funeral.
It's more like telling X's story through Yoshiki's life and that makes sense for this kind of movie, as this was clearly aimed at an international (and new) audience, it's not your average documentary about "they released Blue Blood in 1989 and went on a tour in XYZ cities" type of documentary. Not chronological, and gives little statistics or dry facts. It's more about the emotions than anything else. But it is visually amazing, very well put together, relatable, and if you are sentimental like me, it's gonna make you cry several times. They integrated X's music very well and based on what I read from critics, it pretty much succeeds in introducing this largely unknown band to the West, with pretty high conversion rates of "new fans"
That was the goal I think. Maybe we will get a "normal" X Japan documentary later, aimed at fans' curiosity, who knows.
They did use some nice unique footages from Yoshiki's personal archive.
(On a sidenote, Pata and Heath were never really very open about their lives, childhood or anything, I don't see why they would suddenly open up for a docu crew... Sugizo's life is pretty well documented, check his Wikipedia page
his autobio book also talks a large portion of his childhood, though I could not find an English translation, I read the Russian translation of some of the chapters.)