Tournaments can definitely supplement a players resume but his play in Liiga that year wasn't first overall material, in hindsight.
I don't really blame MTL. It was a tough year to find a real standout and sometimes its a lot easier to be AZ and just say, "okay we will just take the best of who is left"
Sometimes going #1 comes with unfair expectations especially for those draft years where the top guys aren't necessarily slam dunk blue chips. If Slafkovsky had gone #2 to New Jersey, I think people would be a bit more patient.
At least pre-draft, I thought Slaf had some vague similarities to Timo Meier. Timo had the luxury of going back to juniors after being drafted and then had a half season in the AHL. At age 20, Timo had a forgettable start to his NHL career with 3 goals in 34 games. But he got settled in after that.
Sometimes it can be tough for a GM to swallow his pride and send down a top pick. I'm reminded of Adam Larsson struggling in 2013-14. Coaching staff had him playing on egg shells and eventually he was sent to AHL. Eventually it took a coaching change and Larsson was much better/comfortable.