My instant answer: I haven't a clue.
But I have a thought or two. Witnesses see Jesus as unique among spirit beings. He is in God's exact image. Hebrews chapter one says this. He is above all the angels who are commanded to do him obeisance. He is God's ultimate message bearer. He is, as John one says, the one who explains God to us. So Jesus is in a class above angels. Hence he is the archangel. The chief one. But still in the genus Angel.
Just how close that is to Watchtower teaching, I do not know.
Insight vol. one: "As with the visible creation, so also in the invisible realm there is order and rank among the angels. The foremost angel, both in power and authority, is Michael, the archangel. (Da 10:13, 21; 12:1; Jude 9; Re 12:7; see ARCHANGEL; MICHAEL No. 1.) Because of his preeminence and his being called “the great prince who is standing in behalf of the sons of [God’s] people,” he is presumed to be the angel that led Israel through the wilderness. (Ex 23:20-23)"