Why are you assuming Ethel is working in the service sector? Ethel could be an admin assistant in a small office, she could be in marketing, she could be in basic HR. She isn't necessarily working to do something that actually helps Henry. She might be of course.
No one is saying that Ethel should be paid less or that she's somehow less value to society than Henry. But the issue is Ethel thinks that Henry is being unreasonable not wanting to live in a house share at 34 when he is a high earner. The reason that Ethel is able to have the lifestyle she currently has is because Henry is a net contributor to the public purse. Ethel's lifestyle is being subsidized by Henry's taxes. If Ethel stops doing her job, then someone else does it. If enough Ethel's stop doing their jobs, then salaries will increase or cost of living will increase. Henry can absorb that, or if he can't he can decide to move to a cheaper area and take one of those jobs himself. But Ethel can only stop doing her job if she is able to live without a salary coming in, which is only possible because of the benefits system (paid for by Henry). Or if she is sitting on substantial assets that she can sell to fund life without a salary, which would mean she has substantial untaxed wealth.
This is how it should be - we intentionally have a progressive taxation system which means some people are net contributors and some people are net beneficiaries. Ethel isn't necessarily earning less than Henry because she works less hard, and yes some Ethel's are providing core services.
But Ethel needs to accept just how much she needs Henry to keep doing what he's doing. And people saying Henry should move out of London are missing the point that the UK can't afford for him to do that. And we should recognize that if you are in the top 4% of income in the UK, and advise is that you should be living in a house share and shopping at Aldi, something is going very very wrong because thinking you can afford your own flat in London is just unreasonable.
Life gets much, much worse for Ethel if Henry decides that he's going to go and work somewhere else for less money but a better standard of living. But if you were Henry's friend, you'd be telling him to cut his losses and move because it's probably the only way he's going to build up substantial wealth.