The 9900KS is not meaningfully faster than 3900X in any capacity, and especially not enough to warrant its innate platform, feature and price disparity when compared to the Ryzen part.
Promoting often <10% more average FPS as "worth it" over:
Significantly Inferior multi-core performance;
No included cooler;
More expensive, even more so after adequate cooler is purchased;
Inferior platform feature set including PCI-e 4.0 and lack of dedicated Storage lanes on the CPU;
Inferior performance per watt in almost all tasks;
No platform upgrade path; LGA 1200 effectively replaces LGA 1151 next year with no backwards compatibility;
Doesn't even win all games, loses in some titles
Just because you have infinite money doesn't mean you have to be stupid with it. Don't reward this company with your money, because they sure as bloody hell don't deserve it.