I'd say a warranty is a warranty and if the work is covered, then the work should be done. Their profit margin is not your concern. They chose the price to sell it at.
That said , you now own a 10yr old RR, it's value will only go down, expense of repair will not go down at the same speed. These are not cheap vehs to maintain, they are not even reasonable cost vehs to maintain. In the main, even with the help of this forum and others like it, full fat Range Rovers are a money pit. You may enjoy driving it and even fall a little in love with it, but do not for a second think it will ever pay you back what you invest in it.
This is one of the reasons for my initial comment. Make them honour their warranty. Phone Citizens Advice and write down everything they tell you, go back to the dealer and get it fixed. Save your money for the jobs to come, when the warranty runs out or not covered by the warranty.
If you decide to hand it back, why on earth would you buy another car from them? They're not honouring their deal , why would you deal with them again? If the RR seems like she may be more expensive/complicated/trouble than you realised, buy something else from a company who stands by their deal.
Good luck, whichever path you choose.