The end of the second act (in 3-act plays/movies) is either the nadir of the protagonist's journey, or the height of the tragic-hero's success. At least per storytelling books.
Most stories are told in 5 acts [0], and in comedies the hero/protagonist sees the darkest point in the story at the end of the 4th act. Thereby giving the hero the largest contrast possible in climbing out of the depths to their heights at the end of the story; the most cathartic path possible.
In tragedies, the protagonist/tragic-hero sees them at the height of their power/fortunes at the end of the 4th act. Thereby giving the protagonist the greatest fall possible; the most repression for the audience.
[0] The reasons for this going all the way back to Shakespeare and the odd interplay between the size of human bladders (~2.5 hours) and the burn length of the candles from the company near the Globe (~40 minutes).
The book just skips this (which works too IMO, but not suitable for movies; ya gotta show, not tell).
Been several decades since I read Messiah but it ends with Paul walking into the desert abdicating his cause in the destruction he wrought.
Yeah he sticks around for another book (or two? been a while), but the story clearly delineates after the second book IMO.