#2 TNA initially held him back
Before anyone rises to the top of their field they need to run through various stages in order to be considered a major player in their company. AJ Styles faced these sorts of challenges during his time in TNA/Impact Wrestling. When he first joined the company, he was held back and wasn't seen in the same light as other more established talent were.
While the reasons may have ranged from believability to charisma, to mic skills, in retrospect it's hard to believe the man considered the promotion's franchise talent wasn't initially held in especially high regard. The former X-division and TNA Heavyweight champion have certainly come a long way since his early days in the company. As time passed, it is clear that holding Styles back was the wrong decision, and doing so just postponed the inevitable.