If Liverpool had better connections to North Wales such as TfW extending the Chester service to Llandudno, it would be a prime option for connections if we're assuming that the ideal number of connections would be changing trains just once. Whether the demand for Preston to North Wales is there is a separate question entirely, but Liverpool still has connection potential even if it's not quite on the same level as Manchester.Still cannot see why you would go through Liverpool. There is nowhere from Preston where you would travel via Liverpool (except the immediate Liverpool city region). Preston is simply not in the connection set of Liverpool for any other destination.
For Scotland trains specifically, as is what the thread is actually about, I would say the current level of service might be somewhat sufficient. In my single journey experience there and back, most of the passenger demand seemed to be on the core of the West Coast Main Line, especially running southbound. I don't quite know how many passengers would actually be doing a proper end-to-end Liverpool to Glasgow service.