Is that not two different tradeoffs? One is first come first serve and the other is purely if you have the resources at the time? The only people I see that praise the "guarantee if you can afford it", are indeed, the ones that can afford it.
Saying "oh that's just first come first serve" is totally missing the fact that the service level can be woefully inadequate.
What's really crazy is that I live in a small city of about 100k people and there are about a dozen hospitals that I can choose from, first-class trauma centers, multiple renowned research centers (affiliated with three different universities). None of that is counting all of the urgent care and other facilities in the area. I have an order of magnitude more options for treatment than I did when living in New York City...
The only way I could open myself up to more/better care options would be to move to Texas.
You get superb care for the rich and mediocre care for the average guy and very little for the rest.
None of this is to defend the US system in particular, which wildly overspends on the outcomes it achieves. But generally, when it comes to managing chronic and acute health conditions, those outcomes are very good.