I said before he's great in the ring. He can work with anyone and basically any style. Bell-to-bell he's fantastic. No one is disputing that.
He's barely been seen since WM 40. I haven't heard fans chant his name once in his absence. Where are all the "we want Gunther" chants?
To get to the next level, his character needs to evolve from this big monster heel character he's been portraying the past 2+ years. I don't think that is insulting, almost every performer had to evolve to get to the main event level. What makes Gunther any different? Reality is a big dominant monster heel characters typically have a shelf life if they don't evolve. Take Kane for example. As good as his "silent killer' gimmick was, it ran it course eventually.
He doesn't need catchphrases or to cut long promos in the ring. But if he just keeps re-hashing what he's done so far as a dominant monster heel most fans will get bored of it eventually if they aren't getting there already.