Jesus Christ established a new covenant. He is our Paschal lamb. We now celebrate Jesus Christ born in a cave, circumcized in the Temple, rising from the dead, and ascending into heaven. We celebrate Passover at each and every Mass. There is nothing pagan about any of these feast days, all of which fulfill the promises made to but ignored by many Jews.
So since this "new covenant" supersedes and replaces Jewish holidays, why weren't pagan holidays superseded and replaced? Why were they instead "baptized" and made chr*stian? Couldn't Ro'sh HaShanah, the anniversary of the day G-d created Adam and Eve, have been chr*stianized as well as any Celtic harvest festival or Roman fertility festival?
So my original understanding is confirmed: Catholicism/chr*stianity replaces Biblical Jewish holidays and adapts non-Biblical pagan ones.
Oh well. At least you don't have to worry about the ACLU coming down on this holiday!