There's some worrying signs displayed by Slaf.
1. He's often playing "du bout de la palette" instead of skating a bit more to finish a check. He's not always doing that but he's going back and forth between finishing his checks and playing scared. What i don't like is some posters assume it's because he's a cupcake or weak minded or whatever. It could be in fact many things. He could be scared to do mistakes. Maybe he wants to be more than just the next Protas, Cuyle or Knies (all 1.5+ years older than him) because he is a 1st overall and wont settle before 2-3 more years. Maybe it's just lack of experience/stability in stronger leagues he played only 31 games in the liiga and was moved around in junior going from Slovakia to Czechia and then Finland. He moved from league to league and country to country a lot in Europe which was certainly not good for his development early on.
2. He's often not well positioned when he doesn't have the puck. He look lost often when he tries to play a peripheral game. He's at his best when going to the net which he doesn't do on a regular basis enough. Again that's something that is fixable with experience. Most young players look lost early on. Some do for a year, others for 2 and not to rare to even take 3 or 4 years before settling in. It depends. Again slaf coming from weaker leagues and had been moved around a lot certainly did not help. Maybe he'll never figure it out. It happens. But assuming he wont because ... i don't even know why some assume he wont honestly. There's no way to know if he'll be willing to play a north and south game when he settles in and realize he's not the next "MacKinnon". I mean it took Josh Anderson 11 years to figure it out and realise he's not a rtop 6 player

Everyone is different and there's no way to know until the player is in his prime. Anyone who say they know is suffering from the Dunning-Kruger effect.
3. His passes are often too strong and not enough precise. I disagree with people saying he's dumb and can't make a pass. Newhook is dumb and can't make a pass. Slaf's passes are often good and by that i mean the intention is good and the play would have been good if done precisely. But his passes are often too strong, not precise enough pr not in sync with the other player. Again that's something fixable with more experience. Doesn't mean he'll fix it. But that's something he can improve if he works to improve it in practice. I'd rather have a young player who make the right pass with the wrong timing/strength than a young player who make the wrong pass but with the right timing/precision Making a brainless short pass to a player not in a good position is easy to do. Anybody even Josh Gorges can do that.
He's not perfect. But the amount of posters in this thread saying he's never going to be good or better is crazy. At the end of the day we don't know and it will take 2 to 3 more years to know for sure. The first 4 seasons of Jamie Benn were nothing that special and he started his career at 20 years old and had slightly more TOI than Slaf.