What is FR Canon at this point?
We had Ed's original campaign setting prior to the first box. We had the first Grey Box. We had the 2E starting revisions. We had the novels. We had the Time of Troubles. We had more novels - and comics! We had 3E materials, 3.5 materials, the Spellplague, 4E materials and then 5E materials. At each flip of the calendar the lore has changed. Some has been inspired by ideas from new leadership. Some by authors. Some by accident. Some through corporate agendas. There is so much stuff out there - and so much of it contradicts, rewrites or invalidates other parts that it might as well be Star Wars Episodes VII to IX. There are so many disagreements, retcons and errors that there really isn't a single canon. It isn't even close. It is a fuzzy mess - and has been for decades.
Those that love the FR and have memorized more lore than there is in Candlekeep may not find that satisfactory ... but you should all be able to see there is significant truth to it. Being upset about these revisions is about the same as being mad that someone backed over your gerbil again. You can't put the toothpaste back in the tube, my friends.
In the end you're better off approaching it like I do: As inspiration. When I run the FR, I use the Grey Box setting as a reference point - and I modify it to fit my tastes. Some of those modifications are taken from later FR resources - but in the end it is my setting.
Well, not just my setting. My players make real impacts on the setting, and thus it changes from the provided lore... and to respect that, I can't even try to be 'true' to the official canon.