The reason his match with Zayn was so great was because he was fresh out
of Japan and they let him work the style he worked over there. I mean, he was having that caliber of match pretty much every time he stepped in the ring in NJPW. But now he has to work the softer WWE style, and the pacing is much, much different in WWE. He hasn't seemed to adapt that quickly and yeah, it's hurting him. It also doesn't help that he can't really get his point across through a promo because he's difficult to understand and he doesn't speak the language extremely well.
It's not that he's not "that great after all." He's a Japanese wrestler trying to adapt to a completely new style of wrestling in front of a crowd he's rarely worked in front of. Guys like AJ, Owens, and Zayn are much more used to this style than Nakamura is which is why they've caught on much quicker. I'm not saying he's eventually going to catch fire all of the sudden but it's only been a year. People need to give him more time.
WWE isn't really protecting him either. Everyone expected a 5-star match between him and Ziggler at first but it didn't happen. Ziggler's workrate has decreased a lot over the years.
Then comes Mahal and Nakamura, who couldn't afford to lose or was in a position to put someone over, has to put him over. His match with Cena happened at a SD taping which for me was a mistake and I don't remember anything with his matches with Orton.
He then was the 6th most important person in the Kami-Shane feud. Owens, Zayn, Shane, Bryan and Orton all were treated as more important than him.
Then comes the Rumble victory, but then Nakamura does nothing until Fast Lane.
WWE is definately to blame here. Now they turn him heel because he didn't get over as a babyface. Yeah, no shit Sherlock. How could he get over?
Anyway, WWE ruined Nak's character, but the match at Wrestlemania doesn't have anything to do with that. I have watched matches without knowing the build-up before. This was no different. It didn't connect.
First of all the booking of the match was wrong. This is Wrestlemania. This is the WWE championship. But they wrestled like they were fighting for the US Championship. They did the leg angle. You don't do the leg angle in a match 6 hours into a show. Nobody will care about a slow-psychological match this late. That was on WWE entrirely. Still though, it felt like they didn't give it their all.
IMO, WWE gave them a recipe to work with, but the wrong ingredients.