I would ask you that since Puljujarvi and Laine were evenly ranked for most of the year, and that Laine is clearly superior in offense, then what exactly do you think is Puljujarvi's advantage over Laine?
Well, European scouts reportedly were ranking Laine ahead of Puljujärvi(And ahead of Matthews as well, for the record) since before WJC-20s, so I'm not sure how evenly they actually were ranked. American scouts can only judge European skaters so accurately, after all. I'd personally put much more value on European scouts' opinions on players playing in Europe but you are free to judge as you see fit.
Puljujärvi's advantages over Laine are in my opinion:
Skating and overall strength, conditioning and fitness levels. Especially his fitness levels are ridiculous, it wouldn't surprise me at all if he was already among the top in NHL at those. I cannot think of anything else where I'd be confident about having Puljujärvi ahead of Laine.
Here are some that I disagree with but that are pretty commonly stated:
Playmaking, Vision, Two-way play.
But make no mistake. Even if skating was his only advantage, that doesn't necessarily make him a worse player overall. You can do so much with good skating. You can get breakaways and someone like Puljujärvi will score off them. You can actually become a very solid PKer and, again, threaten / force breakaways and get short handed goals. Even if your defensive sense isn't quite as good, being a good skater allows those faults to be forgiven and still allows you to back check in time. When combined with Puljujärvi's fitness levels and endurance, he's sure to be a threat in several different ways. Personally, I feel that this is Puljujärvi's most powerful weapon by far and people who concentrate on playmaking and vision or his shot cannot see the forest for the trees.
And of course, we have to keep in mind that it's entirely possible, even likely, that my judgment is incorrect and Puljujärvi has other advantages as well.