I also agree with Piper not being misused. Without him drawing nuclear heat at the foundation of Hulkamania and the expansion of WWF, things are nowhere near as heated as they were. The Hogan/Piper feud carried over from The War To Settle The Score, which was aired on MTV (big deal back then) and you had several musicians on that show giving their take on the actions of Piper and how they looked forward to Hogan giving him his comeuppance. This, of course, all lead into the original Wrestlemania. Winning a world title wouldn't have made his career somehow better, as heels rarely kept the title back then anyway. Going all the way back to the first ever WWWF world champion with "Nature Boy" Buddy Rogers, heels only kept the championship for maybe a month or two and were seen as simply the champ who transitioned the belt from baby face to baby face. The only exception was Billy Graham in the late 70's. It wouldn't be until Yokozuna in 1993-94 that a heel would keep the strap for several months again.
As for most underused, I'd have to go with Vader as well. Whether it be Shawn Michaels' politics or Vader's injury or a combination of the two, the angle with Psycho Sid winning the title at Survivor Series 1996 and then losing it back to HBK in his hometown at Royal Rumble 1997 was supposed to go to Vader. It was to have carried over from their '96 Summerslam main event and it's the reason the December In Your House that year was called "It's Time", which was Vader's catchphrase.
This could have given Vader a huge main event rub with this, so much so that when the time came for the Austin/Vince story line in '98, Vader could have been one of the opponents Vince used to try and take the belt from Austin. I loved heel Dude Love as well but I imagine an Austin/Vader feud could have been just as good.
