Rowdy Roddy Piper - No. He was the biggest heel in the WWF at a time when it would be silly to take the title off Hogan. Such is luck.
Mr. Perfect - He's my favorite wrestler - but he definitely shouldn't have won it during his second run in the WWF (1988-1991) but his third run when he turned face, him beating Ric Flair for the title in a return match at Survivor Series would've been great.
Owen Hart - There was no time where he could have reasonable won the title. The most over he was in his career was during his return in late 1997, but obviously the were grooming title for Austin, and him winning before Austin would be the dumbest thing they could ever do. 1994 was the other time, but I think they did it right, with having Bret lose the first match and win the return match. I mean, you could've had Owen win the belt at KOTR and Bret win the re-match but I, personally, would not have gone that way.
Vader - This is the most obvious of the list. He was clearly booked to be the next big monster heavyweight champion from his debut. It would've been perfect for him to get the title at SummerSlam 1996 against Shawn Michaels and go on a dominate run until the next big baby face (OR even Shawn Michaels) was ready to hold the belt.