#3. Former WWE Superstar Rusev (Miro)
You only need to look at how the former Rusev, now Miro, is being booked in All Elite Wrestling as their reigning TNT North American Champion to know that WWE were doing something very wrong with him.
Rusev should've been a dominant force in WWE, but he spent his last few months in the company embroiled in a storyline where his real-life and on-screen wife Lana. The Raveshing Russian was having an affair with Bobby Lashley and for some reason, Rusev would lose every match he had against Lashley.
When you look at the work he's doing in AEW as a dominant, aggressive, unstoppable monster, you wonder why WWE had him get cheated on and then lose over and over again.
But, WWE also somehow managed to squander Rusev's comedy side as we saw with the unexpected advent and rise in popularity of "Rusev Day," which became the loudest chant from the audience for quite some time. However, instead of capitalizing on that popularity, Vince McMahon told Rusev he thought fans were 'f***ing with him' and that it was legitimate popularity.