Scouting reports are similar to what you read here. Some scouts thought he had great IQ, others questioned it for various reasons.
I'm in the "I'm super puzzled" category. I've seen clips of Slaf in his draft year and my conclusion was that him skipping levels because of his size made him miss basic hockey teaching (keep your head up, scanning, positioning, etc), but he learned other things just fine like speed shifting to manipulate dmen (he was doing that in Liiga) or his Liiga team systems.
After one season, you can see the improvement with the basic stuff. So his capacity to learn and apply looks good, but his total knowledge and reps his still deficient. It's going to be a slow process but once he's scanning and mapping the ice at a proper speed, we will probably see a bigger jump in his game.