The two worst things that happened to Reigns:
1) Punk's "Make Roman look strong" story on Cabana's podcast (a story based Punk describes a match where he actually went over The Shield (3-1) at TLC. Fan of Punk, but

)
2) Dirt-sheets leading people to believe that he was hand-picked to BEAT Lesnar for the title and people running with it.
You can say what you want about a few of the promos (some were cheesy, some were pretty good), but once people got the idea in their heads that Roman was going to pin Brock for the belt, it was a wash. Another thing that didn't help (which I noticed in the 'Mania thread) is that a lot of cats have no clue how MITB works, so they never figured there was an alternative finish.
What I wonder is that if Reigns wasn't being given a push, how would they have wanted the timeline from the Rumble to 'Mania to work?
If D-Bry had won the Royal Rumble and went on to get thrashed by Lesnar and cashed in on the same way, I'd guarantee that the tune would've been spun to, "They're burying D-Bry! They're using him to get a part-timer over. Seth Rollins is buddies with Triple H, so he gets preferential treatment."