The North Downs route must come high on the list. It should be an important connection between Gatwick Airport and Bristol, South Wales and the West Midlands.
That's what I use it for. The trains are slow, infrequent, often crowded, lack the luggage space needed for airport services. There is one toilet per train, often 'out of use'.
As for Sunday services (remember airports operate 24/7) the last two occasions I attempted to travel from Cheltenham to Gatwick, to arrive by 1245, the line was closed.

When worked as train crew in the 1970s, wages were so low that we were desperate to work on Sundays.
The answer nowadays, basic wages being higher, is the introduction of the Continental Week, ie first week, Mon, Tu off: 2nd week, Wed Thur:, 3rd week Fr Sat Sun. No overtime payments. British Waterways lock-keepers worked this system in th 1960s.

When I want a cup of tea "outside" I don't patronise Starbucks and similar eastablishments. I patronise a cafe that sells tea at what I consider to be a reasonable price. Rail travellers are trapped inside the system until they get to the end of their journey. As to exercising my right not to buy over-priced refreshments, this is difficult when the service falls to pieces and there are long delays. Before privatisation BR^▸ (British Rail(ways)) issued refreshment vouchers to passengers delayed by one hour or over due to the railway's fault. It is now two hours, "to bring us in line with the airlines". When are the railways going to stop trying to ape airlines? There is no reasonable comparison that can be made between train and plane. Thermos flasks are heavy and I don't need extra weight in my hand luggage.
These companies might be privatised but they are supposed to be providing a public service.

In the days of the 'first' Great Western and in the early days of British Railways, station refreshment charges were on a par with those outside. It's ridiculous to say that FGW^▸ (First Great Western) is not responsible for these extortionate charges. They should require the refreshment room operators to charge a reasonable price for basic refreshments, ie tea and sanwiches. Tea from a machine at my local hospital is only 60 pence and I regard anything more than that as robbery.
Stations and airports have just been piling it on over the last few years. It's got to stop.

At many FGW^▸ (First Great Western) stations a small cup of tea is charged at ^1.49. Does any one agree that this is extortionate?

Wetherspoon's charge 99p for a small coffee and if you buy five you get the sixth free.

 Recently at a cafe outside Brighton station I bought a large cup of tea for only 50p.