You're saying that Galchenyuk only had 1 season where he scored more than 20 goals and 50 points, yet the only ones on the roster who had more than 1 season with 20+ goals and 50+ points are Saad, Monahan, Mackinnon and Gaudreau. Only 4 out of the 13 forwards did that.
Also since you're talking about small sample size (Galchenyuk only has 1 season of 20+ goals, 50+ pts), well 5 players among the forwards either played only 1 season or less, and Galchenyuk outproduced them all.
The only ones that are equal or better than Galchenyuk right now are Mackinnon, Hopkins, Scheifele, Saad, Gaudreau, Monahan, and McDavid.
That leaves 6 spots
As good as Eichel is, Galchenyuk did better than him last season. Same goes for Larkin and Jenner.
Then you have Miller, who definitely shouldn't have been in this roster (there are 5+ more players that weren't named, that most people would take over him). Same goes for Couturier
Drouin, who a few months ago was barely in the nhl, and only had a good 17 games (playoffs). His highest goal total in a season or playoffs is 5, and his highest point total is 32.
And finally you have Matthews who did not even play a single professional game, but gets taken (LOL).
I would definitely take Galchenyuk over these last 6 players. And also Galchenyuk is versatile, he can play left wing, center, or even right wing (He played most of his games in the nhl on the left, he is a natural center and plays best there, and he scored most of his goals on the right).