VERY FEW big (6'4") forwards have been drafted first overall or even in the first round. (Big guys drafted high are usually defenders).
Some of those few have succeeded at 18 -- 1. Rick Nash, 6'4" drafted first overall. 2. Vincent Lecavalier, 6'4" 1st overall. 3. Patrik Laine, 6'5" 2nd overall.
Some big forwards drafted high had delayed success.. .
1. Blake Wheeler, 6'5" drafted 5th overall didn't enter the NHL till 22, didn't start averaging over 20 goals a game till age 27. (Now has 8 seasons over 20 goals).
2. Kevin Hayes, 6'4" drafted 24th overall, didn't enter NHL till 22, now averages 20 goals a year.
3. Pete Mahovlich, 6'5", drafted 2nd overall. Had 32 points in his first FIVE NHL seasons. Broke out when he was 25, suddenly scoring 35 goals, after averaging 4 (and had 5 more 30+ seasons).
Tage Thompson, #26 overall, didn't enter the NHL till he was 21, became a regular at 22, scored 8 goals at 24, and broke out with 38 at 25.
Sure, some big forwards drafted in the first round never pan out at all -- e.g., our old picks, McCarron and Tinordi.
Maybe Slaf will be the next McCarron or maybe he'll be the next Tage Thompson. But we can't know that right now so we have to wait.