Here's something interesting: In the old AD&D 2e Cult of the Dragon sourcebook, there's a small section on the Church of Tiamat. It starts off by saying that the church (and Tiamat herself) are little known outside of the Old Empires, but that since the Time of Troubles, Tiamat has felt the need to spread her faith beyond Unther. One way in which she has begun doing that (this is circa 1370 DR) is to infiltrate and co-opt individual Cult of the Dragon cells. Her hope is that the more cultists she wins over, the stronger she'll get and the better she'll be able to take over the bigger cells.
Further to this, it would appear that Severin's divinely-inspired hunt for the dragon masks is not the first time Tiamat has meddled with a leader of the Cult of the Dragon. According to 3.5's
Dragons of Faerûn, Tiamat also subtly guided Sammaster - the original founder of the cult - in his research on the ancient
Dracorage mythal - the permanent epic spell that the ancient elves wove that periodically causes dragons to go berserk. Sammaster succeeded in finding the mythal's capstone (which may have been located near the North Pole, from what I've been able to gather) and corrupt the spell, sending Faerûn's dragons into an ever-intensifying, unending dracorage. His plan was to force all the mighty dragons to accept the transformation into dracoliches or become permanently insane.
At first, this seems counterintuitive to Tiamat's plans. However, I have a feeling she knew he would ultimately be defeated ... and sure enough, a band of adventurers killed Sammaster before his plans could come to fruition. However, they *also* permanently destroyed the mythal, which was no doubt Tiamat's ultimate aim ... because with that spell gone, it meant she could usher in a new Reign of Dragons (the mythal was designed to end the last one, which lasted for six millennia).
Unfortunately for Tiamat, the Spellplague struck a mere decade later. Her homebase of Unther got messed up. Her main guy on the ground, Tchazzar, got imprisoned in the Shadowfell and then got himself killed shortly after making it back to Faerûn. Meanwhile, Bahamut - whose presence in Faerûn had been almost non-existent after his Untheric avatar Marduk was slain a few millennia before - got promoted to a major deity for humanoids (in 4e).
So it was back to the drawing board for Tiamat.
Basically, the point is, the Tyranny of Dragons storyline is *not* an aberration in Realmslore. It is *not* just a copy of the War of the Lance or whatever. It is the culmination of something that's been a long time coming, the seeds of which were planted at least as far back as the publication of the 2e book,
Cult of the Dragon, and which were furthered in 3e's
Dragons of Faerûn.
