Lots of good and thought-provoking answers on here. Thanks for the responses.
Injury: "Ravishing" Rick Rude
Just watched some of his '91 WCW work. That was some top flight work and the spectacular match vs Sting where the injury occurred was supposed to cement him as the top heel and top guy in the company. The laundry list of problems that resulted from the injury (including his eventual passing) could've been avoided with one spot.
Personal: Chris Kanyon
This one is a little tough. Kanyon was peaking at a time where being gay would certainly have raised more eyebrows higher than they do today. Still, his confliction, the stress and anxiety from it, and the drug use that he used to cope left him too erratic to make the most of his prodigious talents. Who betta than Kanyon?
Booking: Big Show
His career has lasted longer than anyone would have guessed considering his size and he's gotten plenty of screen time and title reigns. Still, he was a ready made monster heel turned comedy act and occasional transitional champion. You could see him completely checked out for a stretch of years where he unnaturally smiled and waved like an awkward home schooled kid at freshman orientation because he was resigned to collecting a big check to be an "attraction."
Honorable Mention: Marc Mero
Man, did this guy check off all the boxes in positive and negative qualities. Great look, athletic, legit credentials, not bad at all on promo. Injury prone, drug and marital issues, shit gimmicks and storylines. When you're best known for portraying a gay black man when you're neither and for getting powerbombed by your 110lb wife in a domestic abuse angle, doing acrobatics at 235lbs is only going to end in disaster (listening Apollo Crewes?)