True enough. That said, do the needs of the novels really mandate a Realms Shaking Event every few years? If anything, I would have expected the opposite to be true, as the constant changes make it ever-harder to stay current on the canon. It's not at comic-book levels of insanity just yet, but doesn't it get hard trying to remember if Mystra is alive or dead this week?
Considering most of the plot of Tyranny is coming out of the Adventurers League modules, of which the myriad of players and PCs playing it are probably going to be successful in putting the Cult of the Dragon down (and thus not have much far-reaching effect on Faerun on the whole)... I don't know if we can really consider this a "Realm-Shaking Event".
Is it a pretty big plotline for those in The North and around the Moonsea? Sure. But for everyone else across Faerun... it doesn't sound like there's going to be much of anything Tyranny (and Cult of the Dragon) related. So it appears the Realms might be rather unshooken once the plotline finishes up come February.
Yeah, the issue with RSE wasn't that 'big things' happened in the setting, but that gods died, places were destroyed and so on. I'm pretty sure the ToD storyline -or any future storyline for that matter- won't pull off these kind of things. Or at least I hope so.
Here's the problem. A large number of Realms fans of the books are also D&D players and DMs. So, these people expect to see the game books stay in line with their novels. They think it's cool that when a new D&D book comes out that it mentions that a building in town that was destroyed by Drizzt is destroyed.What I don't understand is, there's already a well-regarded solution to dealing with 're-imaginings' of fictional worlds... alternate timelines. You simply do your Realms Reset and have it take place in an alternate timeline. Then if people want to play in R.A. Salvatore's world they can, but otherwise they can use the 5e shard of the timeline. Easy peasy lemon squeezy.