Regarding Harrogate services - would it be beneficial terminating more Leeds-Harrogate services at Knaresborough? It has a reasonable population (15,000 ish) so a more frequent service from there to Leeds could be justified. It’s also (just) larger than Skipton which has a London service - would it be feasible to start a London train there? If London trains were to be routed via York it’d be a no-brainier calling there of course, although would the platform be long enough?
Look at the figures though - Skipton has far higher rail usage (well over double) - there are a lot of commuters into Leeds and Bradford, and it's the railhead for much of the surrounding area (hence the station car parks being large for a town of the size). The station has four platforms, so more capacity than Harrogate or Knaresborough.