"Overrated" is a term which has to be applied from one person to another person, so saying "is this guy overrated" is necessarily a subjective term depending on who's talking. I think he's valued just about right by the movers and shakers in TNA/IW, and I think that depending on which forum member is talking, he can be over or underrated.
First, you have to understand what AJ Styles is not. He just isn't a tentpole guy that you build a company around. He's gotten the opportunity to prove himself. He received the single greatest microphone worker in the history of professional wrestling as a manager, and people didn't care. He's involved in a cringe-worthy storyline right now that is the definition of a time-killer; people just seem happy that AJ is featured in something, without looking at what this puts him into a position to do afterwards.
If you think AJ Styles should be a world champion carrying TNA/IW, yeah, you're overrating him. That's a job he's had an opportunity at, and he didn't fit the bill.
BIG BOLDFACED HOWEVER- There is a common misconception on these boards that if a guy isn't a WHC or moving in that direction, he's a nobody. Keep in mind that professional wrestling titles aren't prizes that are earned based on you being superior to others in your sport; it's a decision made by television producers in order to create money. There are two hours of Impact! to fill every week. You need supporting events; one match does not make a pay-per-view.
This is where AJ has his true value to TNA/IW. He's a reliable performer who can be counted on night after night. You don't hear about him on the dirt sheets being pulled over for a DUI. He's the Cal Ripken of TNA/IW; not the BEST hitter of his generation, not the BEST fielding shortstop, but pretty damned good at both and as reliable as a Swiss watch.
I'd expect to see him in a lot more of these #2 style storylines. Hopefully, next time the writers will think of something good.