It is actually very unusual to see someone from not so cool promotion compared to giants like One, PFL, Bellator to get so high in UFC from the start. And it is common for guys from other promotion to have a test fights, but after a debut Parnasse is #8 already. Am I underestimating KSW ? (It has been for ages, but I know only Blachowicz and Gamrot) I have never paid much attention to fights, and mostly watched freak fights only. Such as Pudzianowski vs any other huge dude
KSW is, or at least was, the biggest mma organisation in Europe. For some reason, they are not as widely recognised as the organisations you mentioned. They have been criticised for not investing in proper marketing, and maybe that's the primary reason they never expanded outside of Poland/Europe.
But KSW was an incubator for quite a lot of fighters who made it to the UFC, with more or less success. Those who made it big are Blachowicz, Gamrot, Dricus du Plessis, and probably Parnasse.
There are more new ex-KSW sign-ups to make their debut soon. One of them is Roberto Soldic, who was the only man to ever KO Du Plessis. Soldic's debut is scheduled for UFC 332 on 4th October.