Yes, they are certainly rare in captivity, but why someone would believe "the majority" are found in the wild is entirely unclear to me. Wild sighting are exceptionally rare. I'm not aware of anyone trying to count kings in the wild, and doing so would also be near-impossible since it simply is the expression of a very rare recessive gene. As such, the number likely varies drastically over relatively short periods (even in up periods
I doubt there are more than 5 in the wild, and based on extreme rarity of sightings that may well be too much). It depends on the largely random event of a pair carrying the recessive gene breeding, and both passing it on. Of course this is different in captivity where humans can intervene, bringing cheetahs together that likely never would have met under natural conditions.
The thing that unites all these oddities (king cheetah, white tigers, white lions) is that they're the result of rare recessive genes, and all captives originating from very few original carriers; typically a handful or less. You simply can't get any of these without deliberately participating in inbreeding, because both parents have to originate from one of those few bloodlines, which already have been heavily crossed to get the current generation of carriers.
Admittedly I think the white tiger is quite stunning in its appearance, but I can't get past the required inbreeding, or it taking up space that could be used for a pure taxon, e.g. Siberian or Sumatran tiger.
