Removed the "Subverted" sub entry under the Elder Scrolls, here's why.
The pact given by Akatosh applies to any Dragonborn and their descendents. Alessia was the first (reigning) Dragonborn, and while Tiber Septim founded the Third Empire, he was also Dragonborn, which would qualify his descendents as being Dragonblood. As the main distinction between Royal Blood and non Royal blood is time, his descendents were of Royal Blood.
In addition, the Royal Family at the time of the game IS descended from Tiber. The "break" occurred at Cephorus II, however he was more closely related to the septim line than the original heir. While its not exact, a comparison to real world events would have been if the reining house of the Latin Empire (which was a cadet branch of the Capet dynasty of France) had returned to rule France; they would still have been descended from Hugh Capet of France, just not direct descendants of the current ruler.
This trope feels.... problematic.
Naytheism should be the default, not the exception