In hindsight, he shouldn't have been the 1st overall pick. He had a lot of raw talent that made him dominate juniors, but his low hockey IQ prevented him from doing that in the NHL (to this point). His struggles have been exaggerated due to the team he's on, but those struggles aren't completely on playing with the Oilers. He never had the hockey IQ to develop into another Stamkos (like he was projected to be when he was drafted). Obviously, the Oilers had no way of knowing this, but he's a classic case of someone with a bunch of tools but no toolbox.
Could he still become a 40 goal scorer? Yeah, but it will mainly be because of who he'd be playing with. I don't doubt that he'd be a 40 goal scorer on a line with Malkin and on a PP with Crosby, Malkin, Pouliot and Hornqvist, but he'd only put up that many points because of how good his teammates are.