Both Band One solemnities in Rome and Great Feasts in the East, and both manifestations rather than transactions. Neither tradition's own logic separates them.

The Ascension enthrones human nature in heaven, a change in what humanity is. The Annunciation is where that nature is assumed, but it is narrated as promise and consent, not yet accomplishment.

The departure exists to make the sending possible and Acts frames it that way.

Enthronement accomplished over enthronement foreshown.

The Ascension is an event with consequences for what human nature now is. Trinity Sunday is a rubric for thinking about the rest.