For some inspiration of what a First Class service can be, maybe look at the Middle Eastern airlines.
First Class is a good service on the railways if you’re prepared to pay and adjust your expectations suitably. Commuter trains are what they are, there’s not much to mock or complain about other than the lack of policing of them. You don’t want to be paying extra for the space only for it to be oversubscribed with people without valid tickets.
You don’t do First Class for the catering on long distance trains, you do it for a more comfortable seat, more space and maybe a charging point. The catering is too inconsistent between services to really rely on it. Especially on CrossCountry where you can be on a train for 5+ hours with no catering at all.
Then there is the customer service. A few of times staff have created awkward situations for no reason. Once on a York to London service I was asked four times if I was aware I was in First Class then told I needed to present a ticket before I was allowed to sit down. Normally staff warmly greet passengers. On the same line I was denied anything off the trolley despite showing a public rate First Class All Line Rover, because I also my staff pass in my wallet.
Another time on a East Mids service the host streamed straight past me with the trolley and when I raised this with the Train Manager, she rather threateningly said she’d get her to bring the trolley but I’d better not say anything else. A scornful at best approach to service recovery. I was uncomfortable enough with the atmosphere created to move to Standard. Again I was on the First ALR.
Grand Central, the one time I tried them, the carriage was strewn with litter, no hot food or charging points due to a fault, but the carriage was hot due to an aircon defect. The carriage had people who didn’t have a valid ticket (in conversation with each other they revealed they’d move if challenged, which they weren’t) and the guy on the trolley seemed unhappy and unwilling to offer what was on the menu, like juice. Once was enough, I’ve never used Grand Central’s First again.
At Cardiff Central I had the return portion of a London - Cardiff FOR and I was held up at the barriers for a few minutes by a member of staff who decided it had already been used and was searching for evidence of this. It hadn’t been and had been in the ticket wallet for the three weeks since purchase. No marks or damage. Not that he asked, but I frequently passed through the gateline with other tickets after the AM peak, on this occasion it was 7am on a weekday and I decided to use the ticket so I’d have more space to work. I almost missed the train. It wouldn’t be the first time a point was made of getting worse treatment for holding an expensive ticket.
This kind of thing might make a person think “stick First Class, I’m not paying extra to be treated shoddily” but it’s only a tiny minority of staff who make it unpleasant.
Compare and contrast with the airlines. I’ve travelled with British Airways, Cathay Pacific, Emirates, Qatar and Singpore Airlines in First Class. I can categorically state that the staff are never rude, dismissive or outwardly judgemental. Never been accused of fraud for choosing to buy a First Class ticket. And there’s no “best endeavour” approach to the catering - if something is advertised on the menu, it’s available. And they’re always staffed. The railways could do the same if the will was there.
All that said, I do regularly travel in First on GWR between London and Cardiff. The catering consists of drinks and packaged cold food. But the seats are nice, they’re big, they recline and have charging ports. And the staff are always lovely! It’s also policed most of the time so it makes for a very pleasant travel experience.