Like I said earlier, I think you need to consider context last year (which is maybe an argument in itself that he should have been in the AHL, granted), I'm not sure he was as bad and you're making it, but fair enough.
Either way, maybe the borderline thriving you're referring to has something to do with him just being more comfortable, which has a lot to do with having played last year.
I have a difficult time with the argument that there wasn't anything beneficial that he would have learned last year, struggles not withstanding, that he could apply this year.
It is going to become increasIngly difficult for the proponents of sending Slaf down last year to come up with viable justifications if he keeps playing like he has the last 3 weeks really. Tonight he showed he could make real contributions in an away game against a division-winning team.
His assist was a 200 foot play really. It showed his positional awareness, his quickness to get to the defensive zone corner and muscle a guy off the puck, and then show the speed to beat two defenders up ice until he could receive the pass that put him 2 on 1 with Newhook. Finally, he displayed vision and IQ to make the beautiful backhand pass.
On the second Newhook goal, after setting Harris up beautifully for a back door goal opportunity, instead of just admiring the pass, Slaf had the IQ and speed to come flying 85 feet across the ice from the left side boards near the goal-line to the right-wing half-wall to again take away the puck from a Leaf, then got basically the "3rd assist" after seeing the right play and passing to Dach, after which he went straight to the NET-FRONT, further causing havoc and helping Newhook get free for the tip.
In addition to the assist and the play extension leading to our 4th goal, Slaf also got off some shots from dangerous areas, and almost had a similar assist as on Newhook's first, setting up RHP for a close miss.
Who still thinks he isn't picking up the game by playing with NHL teammates and getting NHL coaching? Even after he got hurt last year, he stuck around the team, always asking questions and trying to learn, according to the teammates and staff.
Slaf had the tools at 17 to beat men many of whom were below NHL calibre a bit, but they were still pros and they were still men. This narrative that Slafkovsky was not ready to start his apprenticeship is simply bull. He was, and he did, and he has made noticeable progress to where he looks comfortable in a middle six role already.
Let's stop debating this and enjoy his continued learning. There will be better games and rougher games, for sure, and probably two years before he is a first liner - but the man is an NHL player, no doubt about it.
Q.E.D.