I don't know those lines in any detail, but I suppose it should be on a case-by-case basis. Are the intermediate populations on those lines served by bus on Sundays? But even the Heart of Wales has a service, of sorts! So maybe they should have a claim.
What does amaze me is the differences in provision. I think Cambridge - Ipswich is hourly for most of Sunday, same as a weekday, just doesn't start so early. Sunday trains start from Yeovil Jcn at something like 07.xx - while other locations have nothing until 11.00.
For many years I hoped that some sort of Sunday service could be provided on the Cumbrian Coast - perhaps four trains each way per day, or some such - then Northern introduce a near hourly timetable, though again, understandably not starting so early as on a weekday. (I suppose the theory there is, if you are going to open all the boxes, might as well provide a decent service. Still a pleasant suprise though.)
Against this example, we have the G&SW which Scotrail seems to disown between Dumfries and Kilmarnock on the Sabbath.
NB, all these comments are from memory, and might be in error.