This is counting some carrier-like ships that aren't technically full-blown carriers.

The Australian ships, for example, are "landing helicopter dock" ships. The Japanese ones are "helicopter destroyers" due (due to a prohibition in the Japanese constitution, https://en.wikipedia.org/wiki/Article_9_of_the_Japanese_Cons... some are still being converted to carry the F-35). A number of the American carriers on the list - the USS Wasp, for example - are actually things like "amphibious assault ships".

But even ordering by the penultimate column (leaving only 'aircraft carriers' according to Wikipedia), still leaves the UK and China with two supercarriers each

Which fits with what the original poster stated:

> no country has more than two of them at the moment

Having even one puts you on a pretty small list.