I think the Oilers have mishandled him in the sense that he should have played at least one full season in the minors. The other problem he has that has hindered his success is that he is currently a fundamentally flawed player. he skates well, but is bad positionally, is not good at getting into good scoring areas, he has extremely bad puck handing, and although he has a great shot, he has not shown he has the ability to get into areas he can use it. He has bad decision making abilities when he has the puck, when to pass it, when to dump it into the zone, when to carry it. He is also clumsy and can look uncoordinated at times. He does not make good decisions. Now maybe these areas could improve playing in the minors in a slower game and playing against lesser talent, but those are issues you cant blame the Oilers for. It may be that like Yakupov, that he is a fundamentally flawed player as well. Now if a guy is just simply struggling to score, but skates well, shoots well, can carry the puck, is good positionally, and shows the ability to create plays and make good decisions with the puck, you have much higher hope for progression in his game.
I like Puljujarvi's tools, but he has not been very impressive in his ability to create plays or make any kind of impact when he is on the ice. He seems very lost out there, similar to Yakupov in some ways.