The funny thing is, the MOST Festivus thing in Christmas, is the pagan-origination "Christmas" tree!
Even more interesting is the Winter Solstice was the day selected for the "celebration" of Christ's birth.
Now, one might say the Solstice is 21/22 December, not 25 December. However, at the time 25 December was chosen, they were still using the Julian calendar, which would have placed the Solstice (at the time the date was appointed) as 25 December.
Following that selection, as the Julian calendar was still used, the Solstice began to advance beyond December 25, but the date was set...so it remained the 25th of December divorced from the Solstice thereafter.
Then Pope Gregory came along, and fixed the offset (to keep the calendar aligned with the seasons a la solstices, introducing the Gregorian Calendar (that we use today). December 25 Gregorian was still the date chosen. However, since the Gregorian Calendar had to "reset" the days, the end state put the Solstice back at 21/22 December (Gregorian), with the 25th December remaining Christmas.
All that said, there are still some Christian groups that never adopted the Gregorian calendar, and have used the ever drifting Julian to this day. As of today, there is a 13 day offset. This is why some groups celebrate Christmas on Gregorian Jan 7...which (with their calendar) is Julian Dec 25th.