I’m not the one positing that UHC is so great and every other civilized country has it (ergo, we suck for not having it).

Therefore…comparisons on critical services are 100% fair game.

They're fair game, but you can't make those comparisons against a single country's UHC program for a single procedure. Because it's entirely possible that UHC is generally superior to a private health care system, but that there will exist individual procedures in individual countries where the private system might excel.

To give you your own example, you observed that Canada has far fewer MRI machines than the U.S. per capita - and intimated that this was a problem in UHC. But Japan also has a UHC system, and yet they have more MRI machines per capita than the U.S. If you only look at a single country (and a single facet of that country's health care system), you won't get any useful information. And indeed, just like MRI machines, you can probably find at least one country on each "side" of the matter, so that you can reach contradictory conclusions. Which is why that "single-country single-procedure" approach is not at all useful for evaluating the relative merits of UHC vs. the U.S.' private system.