Jason Robertson is just as slow as Kakko and LaFreniere, possibly slower, and has 37 points in 30 games in his second full NHL season right now.
It's not as simple as just drafting fast guys. This team would draft a good skater projected to score 80 points a season and he'd end up becoming Enver Lisin.
I don't even think it's a drafting issue at this point. It's not like the Rangers went way off the board with Kakko, LaFreniere, Chytil, Kravtsov or Andersson (maybe a tiny bit with Andersson but nothing crazy). This team clearly has a problem developing forwards once we've chosen them and I don't think it's as simple a problem as everyone being a slow skater.
Callahan, Dubinsky, Stepan, JT Miller, and Kreider were all developed well, even though Miller improved with Vancouver. Maybe something changed organizationally but I don't buy that these guys can't develop. Also, Zucc was arguably developed here.