I feel like a guy like Byfield is a good example of a possible trajectory for Slaf (even if Byfield was a better prospect when drafted). Nearly ppg in his third season (short sample though), with lackluster production in his first two seasons (10 pts in 40 games, 22 in 53 games and shorts stints in the AHL). People were saying the same thing as Slaf : akward looking, not assertive enough, not physical, seems to take to much time to process the game, etc.
Bigger guys seem to need time to build up muscles and get use to their body before maximizing their physical attributes. And most player need times to process a higher pace of play.
Like other have said, put him on the first line for 10-15 games and if it's not working send him down in the AHL for a stint where he would be able to adapt to a slower pace and gain confidence if it's not working.
That's the only thing worrying me, that management keeps him to long at the NHL level and stall a bit is development.