How nice that you appreciate my efforts...
You wrote: He quit after 2 years when it cost 200k to train him.
You don't seem like you are that daft, so, Prince William joined HM Forces, went through Sandhurst and Cranwell, and the taxpayer paid, just as they did for my family to be in HM Forces. He trained as a Search and Rescue Pilot, and flew with the RAF for about 4 years, having been in for longer, so did a return of service for the training.
The govt of the day decided to get rid of the Forces doing Search and Rescue and outsourced it to Bristow, so the role in the RAF for being an SAR pilot disappeared. This coincided with the need for William to take on more Royal duties so he left the Forces. RAF pilots could not fly for Bristow, as you can't work for a civvy company as well as being in HM Forces - that should be obvious.
He then went to work for the air ambulance, so he could combine royal duties, young kids and continue to work. After two years he needed to take on more royal duties, the kids were starting school, so they moved back to London.
The Queen has made sure that both her heirs are well away from the capital in Scotland and Norfolk, so if anything happens to her, there is at least one of them available to step in.
You said: Buckingham Palace and Windsor Castle are owned by the Crown - aka the public. You also said in reference to the Cambridges being at Anmer: 'So glad she is enjoying her taxpayer funded stately home whilst we hole up in our flats'. Therefore, you were disputing who owns Anmer.
The President of Switzerland is political; and I suspect that in our system, having a president would muddy the waters, especially if it were someone like Blair, who would not be content to to be wheeled out for ceremonial duties only.
I think that the Crown estate pays a shed load of tax. In 2018 the Crown Estate made £329.4 million (2018) 75% to HM Treasury 25% to The Monarch, so UK PLC doesn't suffer.