I always found the "Mary is actually Isis" talking point funnier than "Jesus is actually Horus", as someone who actually worships Isis. "Sorry Christoids, but the Egyptians have a monopoly on the veneration of maternal figures, and to do it yourselves is literally stealing and you should give it back!"
I always had an inkling of a suspicion that noting common tropes in religions across the world was a point in religion's favor, not against it.
Myth Became Fact:
“The old myth of the Dying God, without ceasing to be myth, comes down from the heaven of legend and imagination to the earth of history. It happens—at a particular date, in a particular place, followed by definable historical consequences. We pass from a Balder or an Osiris, dying nobody knows when or where, to a historical Person crucified (it is all in order) under Pontius Pilate. By becoming fact it does not cease to be myth: that is the miracle. …God is more than a god, not less: Christ is more than Balder, not less. We must not be ashamed of the mythical radiance resting on our theology. We must not be nervous about ‘parallels’ and ‘Pagan Christs’: they ought to be there—it would be a stumbling block if they weren’t.”
That is, for the record, among the most important essays in 20th century theology, alongside the writings of Bonhoeffer and Weil.