#3 Bray Wyatt
Bray Wyatt has shown a lot of potential with his skills in WWE but is yet to reach anywhere near the pinnacle point of his career. He has generally been put in a wrong place for a major portion of his career. He feuded with The Undertaker at Wrestlemania 31, where the "Phenom" was coming out of a shocking loss the previous year and was expected to win.
He lost the title at WrestleMania 33 against Randy Orton which ended his very short reign with the title and was a surprise move by the WWE. If we look at his character and bookings it can be concluded that WWE tried to portray him as the next Undertaker which they have either postponed or have given up on.
But if we imagine him 10 years earlier, he could have got a major push with a great storyline involving Kane, The Undertaker and Triple H who all were full timers that time. He could have had the opponents he needs to accelerate his WWE career right now. Currently, he is the part of Raw tag team championship with "Woken" Matt Hardy which also has the potential to become a stepping stone in his career.