I'll try and be short here: We all know the term “X-Pac Heat”, and obviously it's named after a particular person for a reason, but before there was X-Pac, who would you consider other candidates for “go-away heat”? For me, and I say this as someone who looked forward to GIANT GONZALES matches, I'd throw King Mabel out there. As soon as he won King of the Ring, I had no desire to watch Mabel matches. I didn't want him on PPV. I definitely didn't want him headlining SummerSlam that year. When he disappeared after the '96 Rumble, it was good riddance, nothing of value lost.
The term, though, to me refers to someone who is pushed beyond their perceived station and rejected by the fans as a result. Say what you will about Gonzalez but clearly an 8 foot tall giant is going to be a main event star and everyone realizes it. Same for Mabel, he was terrible but gigantic and fans would at least accept him in that role after a while. For me, the answer pre-Waltman has got to be Dino Bravo in the 86-91 era, who was pushed for no reason and had no heat but kept getting TV time and main event slots despite working the same match for five years and barely being able to take a rollup because he was so stiff. No one wanted to see it, but they kept getting it over and over.