The service is actually quite good these days by historic standards. In the days of the Newcastle > Stranraer working (the heir to the previous long-standing 10:00 Euston > Stranraer meeting the 19:00 Larne boat) the only other train was a Newcastle > Ayr service leaving the Toon at about 17:15.
I was a regular user of the Newcastle > Stranraer (12:55 off Newcastle IIRR, arriving Stranraer at 18:00) when I was at University in Northern Ireland in the early '90s. 5+ hours on that 156 was enough to drive a boy to drink! Prior to that we used the Euston > Stranraer from Lancaster northwards every year on family holidays to NI. That must have been one hell of an ordeal for my parents, travelling from York to Larne with 3 kids! Still, at least we had 1st class privs, and for a few years in the early 80s the connecting Leeds > Lancaster working was a 31 + mk Is rather than the DMU it had been before.