I think it's completely normal to see the market take a different turn towards during the first half of the year. I mean, a lot of people would take profits from the top this Christmas just so they can have a lovely time with their friends and family.
(...)
This kind of reason may valid in previous years of Bitcoin existence, a lot of people also telling that before including me, like if there are more holidays, it may affect the price action Bitcoin, just like before the Chinese new year, "ghost month", the U.S. thanksgiving, and this time, the Christmas holidays and new year.
I'd rather much believe if we have data to use to identify, just like what OP said that it is 'historically', so if we compare the previous Q1 of every year, we can see some bear run on Bitcoin. But this time for me seems different, we are still accumulating below all-time-high, but if ever we the Q1 of 2021 will get worst, I will take it as a pullback or correction for this pretty bull run which we manage to reach the $19,000 levels.