Father Christmas is generally pretty skinny, it is the American version of Santa that is seen as fat.
Father Christmas is an older version of Santa, and one of the ideas that go into our current version. But I was more referring to the difference between Kringle's description in Cold Days/Christmas Eve and The Good People. He is described as being huge like a bear in Cold Days with a big belly. Whereas in The Good People he is basically Vadderung dressed in Kringle's clothes.
I personally lean towards Vadderung being Balor originally; hence Ethniu's solicitation
I have wondered about this. It certainly would fit in a macabre way. Lines like "people you do not get along with" etc make more sense. And it isn't clear on the myths whether Balor had one, two or three eyes. There is also possible Indian and Greek influences on Celtic mythology, so Balor could have been influenced from the Chimaera or Cyclops or even Shiva.
But it seems strange that Ethniu would take over the Fomor or that Vadderung would be allowed to be a part of Winter etc. Also surely if that was his old Eye there would be more than one reference to it.
I think it's more likely she was respecting Odin who was once a very powerful European god and was sad to see he has lost much of his divine power and doesn't see the advantages he has gained.