He has played a total of 5 full NHL seasons.
You don't just take away seasons to skew the numbers to fit your narrative.
His first 3 years he put up 36, 41, 40 points. He had one anomaly season where he put up 71 in 82, then came back down to earth with 53(much closer to his norm). He's likely going to give you 40-55 points in any given season, and as was said, he's not good defensively, doesn't play physical despite his size, and isn't really cut out for C.
And it IS essentially paying almost 10m for his first two years, because you're paying 9.75m in cap space for his first two seasons, and losing a 1st and 2nd round pick to acquire him. The pieces of the deal you proposed can't just be looked at as individual things, they have to be looked at as a whole.
And "possibly put up 30 goals and 70 points"??
He has 16, 14, 14, and 24 goals in 4 of his 5 seasons. The one anomaly season he had 28. Paying for assumed production is never a good thing. You pay for what he's regularly capable of, and that is basically 50 point seasons, give or take a handful of points in either direction. He averages like 50.5 points per season over his career so far. With scoring the way it is in the NHL, I don't think it makes sense to pay that much money, plus draft capital, for a guy who is putting up 50 points per season.
You can sign guys with similar upside in free agency, and not have to worry about losing draft capital. And not only draft capital, but the draft capital that actually has a shot at becoming good NHL players, like your first and second round picks do. You act as if a late first is some kind of nobody pick down in the 4th round.