Pentecost completes the Trinitarian revelation and founds the Church's whole subsequent existence. Theophany reveals the Trinity first, but reveals it to bystanders rather than pouring it out.
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.
Theophany is a manifestation of the whole Trinity at once. The Annunciation is an announcement to one person, however consequential.
Both are disclosures of divinity through a body, but the Jordan discloses it to the world and inaugurates the ministry; Tabor discloses it to three men and is not repeated.
A universal feast attested in every ancient calendar against a dated Latin institution.
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.