As I wrote many times during his draft season I see Slaf as a Malkin/Rantanen hybrid as a prospect. For better comparision let´s see how they were doing when they were in his age.
RANTANEN - he was almost year older because of his late b´day, started season after draft basically as a 19 y.o.
Draft season : Liiga 56 games / 28 points, without international success
D+1 season : NHL : 9 games / 0 points and -7, AHL : 52 games / 60 points
MALKIN
Draft season : KHL : 34 games / 3 goals (12 points)
D+1 season : KHL : 57 games / 12 goals (36 points)
Even Malkin or Rantanen didn´t look like NHL ready or better players than Slafkovsky in that age. So I don´t know why this impatience...
In my opinion, Rantanen´s route looks like the best option for Slaf. It wasn´t the shame if he´ll develop his game in AHL with some NHL taste in 18. Be calm, Slafkovsky is absolutely OK.