I think a lot of it is mental. There were some games where Laf would get 2-3 minutes of PP time. But those games would be few and far between, as most nights he would get 20 second or no time at all. At one point the second unit wasn't even treated AS a PP unit. Gallant sent out the Kid line with two defensemen to cover the last 15-20 seconds.
It's about consistency and being able to get into a groove and build that confidence. That's why top draft picks are spoon-fed minutes early in their careers even when they look like crap at first. They are used to being "the guy" on their team. They are used to having those expectations. On the Rangers, other players had those expectations, and Laf's role has too often been undefined. You can tell when he's in his own head, too, because when he gets in a funk, he stops shooting almost entirely.
Bottom line--the Rangers have screwed up his development. They had one of the best LW's in the league in Panarin, and another, in Kreider, who recently put up a 50 goal season. It's understandable to decide not to supplant one of them with a kid who hadn't proven anything and looked like crap to start his rookie year. But they should have sent him to Hartford to get those minutes and continue to develop as a top-line threat. Laf still shows flashes, and his even-strength production actually isn't far off from where you want it to be. But if they want to have any chance of seeing Laf develop into what he was supposed to be, they need to create space for him on the top line and in the PP and make it clear that winning games is his job and he's not going to be demoted to the bottom six every time he makes a bad play. Players like that NEED that pressure and that freedom. Thus far in NY, Laf has had neither.