Actually, the Protestant denomination the Seventh Day Adventists have been teaching that Jesus is the Archangel Michael, since close to the beginning of the denomination. This is what their chief prophet, Ellen G. White taught. Though she taught that Jesus, the Archangel, is God. So Seventh Day Adventists teach that the Archangel is part of the Trinity.
Charles T. Russell, the founder of the International Bible Students Association, changed this a little, he taught that the Archangel was not God, but the first creation of God. So he taught that God is one, and not 2 or 3 persons. And after he died in 1916, most of them followed Rutherford, and he started changing doctrine, and one day he changed the name to be Jehovah’s Witnesses. But he did not change the basic doctrines about Jesus. So the JW’s have inherited their doctrine about this from Russell. And Russell himself built on the Adventist precedent of calling Jesus the Archangel. But how widely is this believed among the Adventist denominations, outside the SDA, I am not really informed. So it is possible that Russell got this idea from some other Adventists, rather than the SDA.