I think he's had a few solid ones. Ultimate Warrior, The Brood, The Shield, New Day (after a few changes), Bray's characters/Faction, Goldust. Basically I do give them creation rights or assists, if these people can't use that character outside of the WWE.I don't know if Vince was ever a masterful character maker. His biggest stars of the 80s and early 90s were created elsewhere. When Vince raided the territories, the wrestlers took their characters with them. Even Hulkamania started in the AWA. Once Hogan left, the company nearly folded because Vince failed to create a new megastar. I'm the biggest Bret mark there is but he was nowhere near Hogan's level of popularity. The only thing that saved WWF was the Attitude Era. The two biggest stars of that era were Austin, who came up with Stone Cold on his own after being saddled with the Ringmaster gimmick, and Rock, who came up with The Rock on his own after being saddled with Rocky Maivia. Let's not forget WWF wanted to name Stone Cold Chilly McFreeze or Otto von Ruthless.
That's not to say that there haven't been 100% WWE created characters. Undertaker, Million Dollar Man, Kane off the top of my head. But most of the time it's less Kane and more Isaac Yankem, DDS.
But yes - for every successful one, there's 5-20 failures lol, but I suspect that's really no different anywhere.