I don't know what you mean with the Carolina thing, the two teams don't relate whatsoever.
It's the difference of having a 40 PT guy for 10 years opposed to having an 60 pt guy (Kessel will never put up a PPG on Arizona) for 3-4 Years
Then there is POJ that is projected to be a top 4 defender for the next 15 years when Arizona is in need of defensive prospects.
I think you're misrepresenting the situation by using the word projecting. The real term should be probability, because as with basically every prospect there is a likelihood given to every potential outcome. There is a possibility he never plays in the NHL at all and there is a possibility he turns into any average 3rd pairing guy which is basically free on the market (unless you're trying to sign Tyler Myers). I don't see how you possibly can have him projected as a top 4 D, since the Q has plenty and has had even more players producing similar results to him. The Q would produce at least a hundful of NHL top 4 defensemen every year if that was the case.
The Coyotes are in a good spot on their LHD with OEL and Chychrun locking up the top 2 positions for what, 6 more years? OEL has been that team's most important player for at least a handful years, he isn't likely going to be good for 10 more years. You can't present these arguments in a vacuum.
So even with that, Galchenyuk is just a worse Phil Kessel. I probably wouldn't want him on my team for 10 years. The point totals would be very irrelevant if it weren't for the fact that they are very much the same type of player.
Oh and before the 18-19 season Carolina and Arizona were very much in the same spot in a lot of ways. It was before Aho's ascendance into elite player and before Keller's sophomore slump. These teams seem very bad until they one day start competing. Arizona wasn't even bad last year and were, again, very injury plagued. It wouldn't surprise me at all if they made the playoffs this year, and it wouldn't have last year.