Ambrose is a great IC level guy. Or rather what the IC meant circa 1992. He can convincingly have main event feuds as well as working with the mid card, but probably shouldn't hold the belt for a long time. His flaws have more to do with booking than ability (although some of it is on him). Doing the rope fake out thing every match is tired, his punches look weak, and "creative" has made him far too goofy. I like Ambrose, but I'm not going to go to bat for him being a long serving WWE champ.
He is still a good worker, though. Reigns being athletic is fine, but it doesn't really help him have a good match. Clearing the rope on a dive is cool. If it were a track and field competition he would earn high marks, but wrestling needs more than just doing athletic things.
As far as being a wrestler goes, he is well below Cesaro, Seamus, and Wade. And like I said, being a good wrestler isn't the only thing that goes into getting over, but he doesn't have much of anything else to make up for it. It's not a smark conspiracy to take him down, IMO. They like to get themselves over and he is certainly taking the brunt of that, but even when the crowd isn't overly smarky he gets a worse reaction; silence.