I don't see what problem the SA stopover is, apart from it being better done at Cape Town rather than Jo'burg (where many tourists arrive anyway). The comparable distance offshore Galapagos Islands in the Pacific have multiple daily tourist jet flights from Guayaquil in Ecuador, far less accessible than Jo'burg, yet seem to manage quite straightforwardly for European tourists.
If you don't want to stop over in Jo'burg the Saturday departure connects quite nicely with incoming European overnight flights, and when it gets back the same applies with the evening departures back to Europe. It's well under 24 hours from London to St Helena.
This money came out of the overseas aid budget, the same budget that gives money to the Indians despite them having a space budget. If the money has to be spent I would rather see a British dependency get it than India
Apart from this being a poor attitude to UK public spending, the money was almost wholly spent with a South African contractor with SA labour and materials.