In my opinion, more innovations (which the rest of the world’s public systems do benefit from), better customer service, better patient care (far fewer rude or abusive nurses and doctors), higher standards (quality of facilities and attention to detail and time spent with patient), flexibility (between providers, in scheduling, and even in the care/procedures you receive), etc. Oh and the ability to receive the care you are willing to pay for at all, instead of being denied. I do think there are lots of flaws too but feel they’re addressable with targeted legislation instead of some massive change.

Nope. The GP asserted something without evidence so I am engaging with that same standard.

What makes you think "every other developed nation" has higher quality (and single-payer) healthcare systems?