How do you know Christmas simply didn't align itself to those holidays themselves, because after all, a year end winter feast is nothing new in history? Or that the traditions we have today may have at once been part of such syncreticization but then died out until the modern day? In other words we don't necessarily have to see such traditions today per se for Christmas to have absorbed them over its time.
We don't. But we also don't know that they were, and we don't have enough quality evidence in favor of that hypothesis to justify the confidence with which it is asserted.
In the absence of evidence about the timing being affected by other festivals and in the presence of much evidence that all the actual traditions are far more recent than pagan, I don't believe it's fair to claim Christmas has pagan origins. The absolute best we can do is say that its timing may have been influenced by other, pre-Christian celebrations.
I agree but I also would be interested to see any proof for the claims you're talking about with regards to Christmas not having any pagan roots, where are you finding this information or rather, where can I read more?
I linked one example—a video on Christmas trees from a religious studies scholar. They have similar content on the date of Christmas, and there are plenty of sources on each other tradition.
Here's another one on Saturnalia from the same scholar:
One small exception
Russian empire turned a figure from Pagan mythology into a St Claus like figure
https://en.wikipedia.org/wiki/Ded_Moroz
But my understanding is that him handing out gifts didn't come from Pagan traditions and was a result of largely copying Santa Claus traits.
Later during Soviet times secularish Christmas traditions including Ded Moroz were moved to New Year's.
