Dean Ambrose is hands down the most overrated guy on the roster. People were actually hyping that dipshyt up as the second coming of Stone Cold Steve Austin and saying he should have main evented Wrestlemania.
It's not all his fault, because WWE is terrible at booking faces in general (as evidenced by all of the Shield members flopping during their face runs), but Ambrose doesn't make things better with mediocre matches. If you really look at it last year Reigns had better matches last year than Ambrose did often with the same opponents.
Second runner up is probably Bray Wyatt. After he makes his entrance shyt starts going downhill fast. His promos don't mean anything anymore, he's never had a great match, and his feuds are always nonsensical bullshyt. The potential to be great is there, but WWE booking basically has him in the same spot as New Day.