Even if it was 'hijacked' from the pagans, it certainly wouldn't have been hijacked from
Germanic pagans.
There are 4 common explanations advanced (imo the last one best fits the available evidence):
1. Saturnalia appropriation
2. Sol Invictus appropriation
3. Calculation thesis (9 months from the annunciation)
4. Equinox was an actual event long seen as auspicious hence it being marked in countless traditions. Christmas was on equinox for the same reasons pagan festivals were (25th
despite pagan association, not because of them).
It's true that it took centuries to develop and many early Christians rejected celebrating the day of Jesus' birth, it's also true that at some point they changed their mind on this.
The idea it was mendaciously 'hijacked' is problematic though as Christmas on the 25th Dec seems to have emerged in the late 3rd/4th C at a time when Christians were still being persecuted as a religious minority who refused to assimilate (also there are no sources from that time complaining about certain sects 'hijacking' a pagan festival).
Ironically, like many of the anti-Christian arguments made by contemporary atheists, they have their roots in Protestant anti-Catholic polemics, and calling them pagans was a favourite tactic. As for factual accuracy, it's a bit like putting your faith in the 16th C version of Fox news
Anyway, puritans didn't ban Christmas for being Pagan, they banned the celebration of Christmas for encouraging immoral behaviour and distracting people from religious obligation.