I may have just been in a bad mood, but this book just felt like total glurge to me. Little boy and little girl help an unfortunate Santa who has run into trouble, and as a reward the boy gets out of the tropical Christmas that his parents wanted. A very quick read at least.
The only one of these I’ve read is “Hadrian the Seventh”, and even though I have a weakness for peculiar 19th and early 20th C novels on religious themes (I actually really enjoyed Newman’s “Callista”), I can’t really disagree with your assessment. Vicar of Christ sounds like I might quite enjoy it, though.