^ These comparisons which one will be "better" down the road are just futile and off the mark.
First, nobody can tell at his point. Secondly, define "better". Yes, it depends.Thirdly (and related to the point 2), they are all great prospects and young players with different strengths and weaknesses and styles. -And will have different kind of development curves.
And fourthly, there is hardly a non-biased poster making these strong claims in one or other direction which will have its "ripple effect" here.
After saying all this I must, however, make my corrective assessment of this "situation" (taking into account all the above listed revisions):
Barkov is not as "boring" player as rumor has it. The more and more comfortable he feels and looks out there the more and more interesting he looks out there. His skating has improved already by leaps and pounds from what it was last season; and he seems to be about "ready" to make some pretty flashy plays: I have seen first signs of this. Nifty little dangles on 1-on-1 etc.
Secondly, while MacKinnon might be more productive - Barkov won't be a slouch point wise, either; he should be capable to reach PPG level with good line mates in a couple of years.
Thirdly, Drouin could very well be the best of the draft offensively, measured in point totals. It's not a stretch at all. And Jones is a Dman - so, why to compare him and Barkov at all. He should be really good, too. You cannot say "Barkov will surely be better than Jones" - or it doesn't make sense anyway.
Fourthly, Barkov will be the best Finnish forward in two years barring a serious injury - and the best player of his draft class - in the non-sense sense one should read as: I HOPE that Barkov will be the best player of his draft class -even though the notion "best" needs to be defined here.