I'd say Caernarfon is a much better bet for tourism than Okehampton, with the castle, WHR and surrounding tourist attractions, and there would be good potential for rail especially if they could get the track past the supermarket into a more central station. The charters on Borders Rail show what can be done with minimum extra infrastructure and a bit of imagination.
Don't bring Borders into this - that case was entirely different.
As I've pointed out many, many times, the issue for Borders was towns like Galashiels, Hawick etc were then put 30-40 miles away from the nearest rail station and even the road journey to the nearest main place was a long and difficult one. Caernarfon is 9 miles to Bangor and 30 mins by bus. Galashiels is over 30 miles to Edinburgh, the X95 takes 90 mins to cover that journey.
People are quick to point out the success of Borders Rail and claim it's a guarantee that other schemes will be similarly successful. The Robin Hood line is a good example - Mansfield once cited as the largest town without a station of over 100,000 people is only now nudging 400k use a year - Stamford, population 20,000 achieves a similar number.
The question is who would use the train to Bangor from Caernarfon ? Is it tourists ? then there's unlikely to be sufficient to make this worthwhile. Is it locals ? Is there the demand - bus pass holders won't move over because they would have to pay. Locals with a car ? Well, it's only 20 mins to drive to Bangor, so unless they live 'on top' of the station, it's going to be slower.
You think the bus industry is the best judge of what constitutes a good bus service? Seriously?
If that's the approach we might as well all give up and buy cars.
I think all the main operators have examples of good services - Stagecoach across Northants do a good job. Go Ahead in various areas have good operations. First seem to have turned a corner. And Arriva (despite your dislike of them) seem to have several areas where they have sustained a decent network running at sensible frequencies.
Perhaps if you think it's so easy, you should start a bus operation up and show us how easy it is and how it should be done, rather than just carping from the sidelines. Put your money (and alleged knowledge) where your mouth is.