There was a Soroasterian element. The worshipers would make a throne for the G-d and set it for fire, so none could sit there but the G-d, even G-d the Father.
What happened is the stars moved. G-d the Father created the solstice in the consellation of Taurus. Moving the Heavens required a new dispensation, and Mithras was the name for the G-d which moved the heavens, so that the winter solstice moved from Taurus. Thus Mithras slayed the Bull.
Christianity adopted this all-powerful figure as Jesus...Even giving Jesus the Birthday of Mithras (just after the Saturnalia), with his new dispensation in harmony with the old as a favored son would be in harmony with the father.
Mithraeums had starry displays, to explain this to the acolytes.
Christ is the Second Person of the Holy Trinity. He entered the world during the time of the Roman Empire, becoming one of us. He died for our sins and rose again from the dead.
These things were not done in a corner. We know far more about the words and deeds of Jesus the Christ of God than we know about any other historical figure before the invention of the printing press.
Identifying Christ with the Mithraic Bull cult just because we took over a pagan holiday is a ludicrous act of God-denial.