Sheamus wasn't just overshadowed to the Authority. Unlike Orton and Rollins, he is just boring and has little to offer when it comes to personality. Rollins and Orton at least had/have that, more than Sheamus anyway. Simply aligning a not-so-charming wrestler with The Authority never means that the said wrestler is automatically going to become a top heel, face, or top anything. We've already seen that when Curtis Axel was aligned with Paul Heyman, haven't we ? And in the first place, anyone with the potential to be the "top heel" of their time/brand/era (Punk, Jericho, Edge, and now Kevin Owens), never really needs such an alignment. Kevin Owens is the best exemplar of that. So in his case, being with The Authority actually saved Sheamus, lest people should have begun throwing eggs in the ring after 3 weeks of having heard him say "5.15" .
The long-term plan was never about Sheamus. Only Roman Reigns. He just happened to be there during an injury-depleted roster, with a MITB briefcase as well. The WWE, thanks to the ever-declining ratings and a stagnant as fuck product, decided to bring in Vince, and lo and behold, things seem better now! We don't even have to watch another Roman Reigns and Sheamus match at the Royal Rumble now.
I had recently been stuck in the "sheamus sucks" mindset throughout december, so I totally failed to derive any fun out of his in-ring performance, which is pretty solid IMO. It's only as a laughing Irishman repeating "5.15" that he's boring as fuck. I sort of prefer him when he gets intense, like against Dean Ambrose on Raw, near the apron when he threw Dean onto the announce table? And watching that match made me realize how good a wrestler Sheamus is, and how effective, as an intense/furious Irishman. It helped me get out of the "Sheamus sucks so avoid all his matches" trap!
I still think he never was or came across to me as a legitimate maineventer, just like Alberto Del Rio. I'm not sure he ever will. We don't quite know if the WWE will push him in the mainevents again. That only means we'll see him competing in the upper-midcard, or at times floundering in obscure waters. It's not a bad thing. Even Randy Orton has been going through that, though Randy is on a totally different level as a wrestler, performer, and persona.