The WCT tour was a big diversion from the ITF. The two entities went to war over who would play where. The ITF was against paying the players after everything went Open in 1968. Lamar Hunt started the WCT as an alternative and to promote professional tennis. I think his first round prize money was $5000 which was about half of what a player would make if they won a Grand Slam.
But, I don't know that a WCT 8-man event was as tough to win as a Grand Slam. For sure it was more interesting and had the top players, except for Ashe who opposed the whole thing (why?). It is for that reason that I don't give as much creedence to the WCT as a Grand Slam although I really used to love the WCT events.