I'd say he's an above average passer who can make himself look average in certain games, and "poor" if you choose to highlight only his bad plays.

He can be a little hesitant in decision-making at times which leads to the some of the poorly thrown deep balls that you were talking about. I would tend to agree with you that his completion % is higher because of the nature of their play-calling last year and can OCCASIONALLY bullet a pass to a receiver from <10 yards away, a la Michael Vick. 

That being said, he has the 4th highest returning adjusted completion % this year (accounting for WR drops, Huntley's WRs had 3rd highest among returning FBS starting QBs). Very, very few of the drops are because of his throws. The WRs had trouble last year hanging on to some easy balls (e.g. Dixon in the ASU game that was a beautifully placed deep ball that should have been easily caught for a TD). He also plays for Utah, so there just aren't that many deep ball opportunities, but he has actually been pretty solid when throwing beyond 15 yards (30% of his completions against BYU in 2017 were > than the 15 yard mark you mentioned he struggles at). You can pinpoint a few plays that he overthrew his receiver on the deep ball, but there are a lot of plays where he puts it exactly where it needs to be (Demari Simpkins in the AZ game/Nacua in the Stanford game). He also takes pretty decent care of the ball. He led all P12 QBs with the fewest turnover worthy plays last year. 

Like I said, I'm not saying he's this spectacular passer but he is MUCH better than you are giving him credit for. There are actual metrics and legitimate college football analysts that will tell you that. I don't need to make a statement based off opinion. Although, apparently mine would be legitimate because I spent years "working with QB coaches"