Is the role of the Last Dragonborn in the world comparable to Wulfharth or Morihaus? It's sort of related to a mod idea I have where the LDB joins two other people who fill roles similar to Alessia and Pelinal in a fight against the Thalmor, sort of reenacting the Allessian Rebellion

Who does he help that act as Alessia and Pelinal?

Wulfharth? Sure.. I mean according to one legend Wulfharth watched Shor's ghost battle Alduin's ghost and then learned a time-breaking Thu'um from it. Kinda like when the LDB watched the Tongues battle Alduin in the time-wound and learned Dragonrend. There's also the thing about Wulfharth and LDB both being Dragonborn/Shezzarine.