I don't feel I should make much of an effort to defend something that seems to me just plain bad writing

But here goes:
Before Christianity came to the British Isles, there were various pagan beliefs, often to do with sex, fertility, rejuvenation and so on. Their rites were flamboyant and colourful - which made them difficult to replace with Christianity. The way a compromise was reached was that the cycle of Christian festivals was made to accommodate the pagan ones. There was already a pagan Winter Solstice festival towards the end of December, so it morphed into Christmas. But Christmas festivities nowadays, while not honouring any pagan belief, are rich in the flamboyance and colour of the original pagan feast.
I think the sentence that's bothering you is using
pagan to refer to flamboyance and colourfulness. But I think it ("pagan") is poorly chosen in this passage, because pagan festivities and sex-oriented dancing have a lot in common: "Saturday Night Fever" is, in that sense, already "pagan". The writer is showing off - using "a sort of pagan" to suggest an analysis that just doesn't hold water.
b