Ignoring that fact that I can find no credible historian or mythologist who makes a similar connection, we can proceed assuming the validity of the claim.
Historians have made a connection between Jesus and Horus-Osiris, where Horus-Osiris (an older character than the Jesus character) is called Priest, Prophet, and King, and calls himself “the way, the truth, and the life”.
We have the Mithra myth, which preceded Jesus, talking of a god (Estra) who was born near the day we celebrate as Christmas, who died, and was born again three days later on Easter (Estra, Easter).
But this does not invalidate the Christian claim. Rather, it supports the claim. For all the other myths are dead, and few believe in them anymore.
The Truth has survived and thrived, and it is likely that people, sensing in the visible world what the invisible world should show, before it even occurred, made up myths that parallel the Truth.
People wanted a savior before Christ, the whole world ached for Jesus, so they invented one.
Plato himself states in his laws that “The Search for Truth begins with the search for the God-Man.”
And this God-Man must have had a woman greater than all the other servants of God, than all the other angels, the seraphim and cherubim, to bring Him into the world.
Where we see the archetype of Christ, we see the archetype of Mary (Isis is the typical connection I always encounter).
And so with the evidence from myth of Christ in all cultures, we hold up the real Christ as the answer to all that the myths seek to explain.
And as we see Mary in the myths of the past, we can hold up the true Theotokos, the true God-bearer, as the answer to the shadows mythmakers beforehand drew.
In their attempts to explain, even the pagan ancestors, in their attempts to understand, touched brilliantly upon the Truth revealed most fully in Catholic Tradition.
