I don't think John Moxley sucks at all. In my opinion, I think the guy is great. He has decent ring skills, knows how to brawl, has in ring mentally aka psychology. He one of the better talkers in AEW at the moment. Has a great character for the company.
I don't think he got demoded at all or even failure in the WWE. The only failure I see from the get go was WWE. They just can never book him right like so many of their other talents in the company. John Moxely did almost everything that there is to do in the company. He won the WWE title, beat his 2 Shield Mates back to back during the summer of 2016. Was first drafted to SD Live to boot. Was the longest US Champions in 2014, won the IC belt. Also won the tag titles many times in his tenor there. What was left to do? The joke 24/7? Royal Rumble victory? Win in the main event at WM? The dude basically did everything. There nothing else but to move on.
Clearly the guy wasn't happy in the WWE which took a tole on him mentally and emotionally. In 10 years from now John Moxely will be known as the guy that basically took a big time chance on himself and look what it got him? A title in NJPW and the main belt last year in AEW. He will be hall of famer not only in WWE but also in AEW. Will he ever go back to WWE? Most likely if they can come to an agreement. The guy is still hungry and ready go further in his career. If I was in his shoes, I would have done the same damn thing. And the guy gain a lot of respect for honoring his contract in WWE and left.
Sometimes it's just better to follow your heart, mentality and intelligence.