Theorizing is great, but in practice Kyokushin matches are a whole 'nother animal. Muay Thai itself has a whole different strategy than MMA striking, but I think it much closer approximates it than KK.
KK matches are basically a blitz on who is the toughest and can hit hardest. I'm not ragging on technique, because KK can be very technical, but when a knockdown or backing up results in an automatic loss, you really have to tailor your strategy to suit the rules. I'm not even gonna go into the "no head shots" rule, because that obviously changes the game completely. Exactly as a guy said before, the range and strategy in KK is different than any other sport out there. Just watch any match and realize it looks completely different than any kickboxing/MMA.
Even the KK greats like Hug and Filho had to deal with inferior boxing through their whole careers, and those are two of the best KK fighters of all time. If you're gonna bring up Schilt, I think the more relevant discussion is his massive reach advantage rather than any specific style he trained in. The guy could be a Kung Fu fighter for all we know, his jabs basically beat out any punch in the sport. Are we gonna say "Karate training taught Semmy how to stick his giant hand out and KO people from 10 feet away"?
As for Judo, it's a great overall grappling style, but a vast number of their techniques are gi dependent. Everyone says "you can adapt it" but that's basically eliminating all types of setups, footwork, chains and grip fighting strategy in favor of basic over/under hook clinches. If you do that, why not just train wrestling? Why not save your time learning 20 different entrances and grips you'll never use for a seionage when you could go to wrestling practice and learn the arm throw without any no-gi modifications or adaptation?
Not only that, but a lot of the throws are so Ippon-focused that they favor velocity and landing a clean point over control, which basically lands you in a shitty positio. That's why you see Karo, supposedly one of the best-adapted Judo MMA fighters, having a higher percentage of landing in a good position with a basic double leg than he does with his Judo throws (why would you throw someone just to end up on the bottom?) And sure, they have groundwork too, but if you're focusing on MMA, why not just learn from the best, who are most clearly the BJJ guys?