The primordial feast day outranks the culturally dominant one. Sunday is the Resurrection kept fifty-two times a year; Christmas is kept once and was not kept at all for three centuries.

The Incarnation is the premise the Resurrection needs; Pentecost is its application. Premise before application, though this is the closest call in the upper half.

The headline claim and the inversion the scholarship keeps warning about. Augustine's distinction in Letter 55 is that the Nativity is commemorative while Pascha is sacramental, a transitus the believer actually enters. Cultural weight runs the other way, which is the problem and not the evidence.

The birth of Christ against the death of his mother. Not close on any tradition's reckoning, whatever the Dormition fast implies about devotional intensity.

Both are feasts of manifestation, and the Nativity is the manifestation the other one interprets. Narrow, and in the East it would go the other way.