WWE is the number 1 promotion around, as such many of the top stars would have often gone through the WWE developmental and possibly even TV due to WWE looking out for people who are good at the business.
Having said that, WWE also has many creative issues (as seen by the sliding ratings and the crappy at times product) so it is no wonder that many people never have their talent used fully by WWE.
RVD for one, Dreamer, Christian, Anderson, Pope, Haas and so on.
Each one of those was liked by the fans, could/can put on a decent match and a decent promo.
And yet, none of them were given a fair shot by WWE - due to giving them silly gimmicks, silly story lines and so on.
Haas himself has stated that in a recent interview
As for botches in the ring, Batista botches and yet he is still main event (and rightly so).
Anderson is not that bad, his matches in TNA have been fairly good.