I loved the unreliable narrator as it gave DM's much more leeway in the face of players who were also Realms junkies. With the unreliable narrator it was much easier to change/skip lore without having to hear the complaints about how "it isn't the Realms if blank didn't happen" etc. The reliable narrator basically tells DM's that if you don't have this cannon and reliable lore in your Realms, then your Realms aren't really the Realms anymore but some odd hybrid.
Some FR authors are quite obviously well aware of the "rules" and "stories" in the Realms *and* able to carefully fashion their writings so that they are ambiguous/mysterious to those unaware of the rules yet stated/defined correctly to those who want to know how the events in the stories would be reduced to terms of game mechanics. It's quite apparent that many of the better FR authors have played the game and could be counted among its most ardent fans. Then again, it's quite apparent that some FR authors possess less literary skill, are more constrained by Wizbro dictates, or quite simply haven't got a clue what the D&D is really about, a few even write more generic fantasy which is butchered into minimal compliance with a Realms-compatible format. I won't name any names because those authors I would consider best in this regard will already know who they are.