Heavily Christianised, along with contextual racism, xenophobia, animal cruelty, religious bigotry towards paganism and of course any story involving Black Pete and mentioning how good Santa Klaas was to 'the good slaves' is difficult to read. Taken in context, these are still tales of cultural and religious erasure, colonialism, superior attitudes and a level of racism that can be - even keeping in mind the time in which they were written (1918) - disturbing to parse.
I still like fairy tales like this because they situate the perspectives of the time and the place, and they also don't pretend that this isn't the heritage, or handwave it away, or make it seem like it wasn't that bad at the time when it was. I was most fascinated hearing about the hints of Pagan druidry and similar, but they are largely only hints, and in many cases all of these figures die to make way for Christianity, saints, and farms. These fairy tales are dark not because they're particularly grotesque, but because they show us that in many ways, we actually haven't come that far from these roots, and we have a long way to go.