Just out of interest, do you know of instances in Watchtower publications where they state that Jesus is an angel? I went looking a few years ago and didn’t find very many examples.
They definitely teach that Jesus is Michael the archangel, i.e. ‘ruler of the angels’ but they tend to emphasise the ‘arch’ or ruler part, and don’t often say that Jesus is ‘an angel’, as simple as that.
JWs seem to teach that Jesus is a unique case. He is an angel in the sense that he is a spirit creature in heaven who is distinguished from God because he had a beginning. But he is unlike the angels in that he was the one sole creation of God alone, everything else being created by God through Jesus. So I guess that’s where it’s coming from in the 1991 Watchtower when it said that God didn’t send “some angel”, he sent his “only-begotten Son”.