The Barnstaple line timetable does focus on serving the intermediate stations where there is some modest custom over the ones where there is virtually nil custom. This is I presume because it wouldn't be feasible to run an hourly clockface service serving all stations, but it makes perfect sense. The stops at Crediton and Eggesford are compulsory due to the loops, although Crediton is the only town directly served, and Eggesford serves Chulmleigh in any case. Yeoford, Copplestone, Lapford and Umberleigh stations are in or adjacent to the villages they serve. Morchard Road is as the name suggests some way from the village, but does have other nearby villages to serve.
Kings Nympton, Portsmouth Arms and Chapelton in comparison have virtually no local population to serve. It surprises me that no attempts to 'modify the Tarka Line by closing them in the 1960s were made given the line wasn't listed for closure in the Beeching Report, although it has I believe been under threat at times since. Newton St Cyres is also some way from the village and the bus into Exeter has long been more convenient. Consequently it makes sense to focus on the other stations.
There are in any case additional services on Saturday evenings at Newton St Cyres and Portsmouth Arms, given the fact there is more custom at that time of the week due to the Beer Engine, and whatever the pub at Portsmouth Arms is called.
I do tend to the view that reducing services to lightly used stations (even if not necessarily closing them) could benefit many more people than it disadvantages. The Cambrian Coast route to Pwlheli has 28 stations in 57 miles and takes 140 minutes. Many of them are request stops. I don't know the area, but is it necessary to serve every single one of them on all services? I know the line speed isn't very high, but surely cutting out a few stops could improve the journey time.
Along the same lines as
@zwk500's mention of Balcombe, there are 11 intermediate stations in 13 miles between Brighton and Goring-by-Sea. Given it's a 2 track line which is basically impossible to expand due to urban sprawl along the entire route, would it be unreasonable to reduce some stations to a parliamentary frequency? Several stations are less than 1.5 miles from the next one, so it wouldn't seem to massively deprive anyone of access to public transport. Currently the line attempts to be both something of a metro between Worthing and Brighton, but also a longer distance route between Southampton / Portsmouth and Brighton. This means journey times on the longer distance routes are not particularly impressive. Having a few longer gaps between stations might help.
As always, the question is at what point the needs of the many outweigh the needs of the few.
Back in the 1990's and before, you had fast services from Brighton to Portsmouth or Southampton, which would stop at Hove, Worthing, Barnham and Chichester. After which you would have local service from Brighton to Worthing/Littlehampton stopping all stations. You would also have a stopping Littlehampton to Portsmouth & Southsea.
The path of the fast services got taken away, when GWR had their services which went to Brighton. The following is what I believe should happen:
05:00 Brighton to Portsmouth Harbour stopping at Worthing, Barnham, Chichester, Havant, Fratton, Portsmouth & Southsea, Portsmouth Harbour
05:05 Brighton to Southampton stopping at Worthing, Barnham, Chichester, Havant, Cosham, Fareham, Sputhampton Central
05:10 Brighton to Littlehampton all stops service
05:20 Brighton to Portsmouth & Southsea all stops service
05:27 Brighton to Southampton all stops service
06:00 Brighton to Portsmouth Harbour stopping at Worthing, Barnham, Chichester, Havant, Fratton, Portsmouth & Southsea, Portsmouth Harbour
06:05 Brighton to Southampton stopping at Worthing, Barnham, Chichester, Havant, Cosham, Fareham, Sputhampton Central
I would not bother with the services to West Worthing, as this would be served by the stopping services.
But from reading the comment below from the wiki page
https://en.wikipedia.org/wiki/West_Coastway_line for the West Coastway route, I think going forward you are going to see even more stopping services, than you have now:
"It is now proposed by Southern to shake up the service pattern in the region, by diverting all the services from Southampton Central to London Victoria to Portsmouth Harbour, as well as diverting all Portsmouth Harbour to Brighton services to Southampton Central and with an additional stop at
Woolston. If all is successful, these new changes would come into effect in May 2024."