Too many things wrong with your reasoning here to list. Hartman's offensive game isn't what sets him apart, but there is plenty of upside there. For me, he looks like a good second line prospect, a 25/25/150 PIM sort of player; the type of guy that we had a ton of success with this year. Comparing Mantha to Picard is only fair in the essence that both are big, skilled wingers who put up a ton of shots on goal in their draft year. The difference is, Mantha scored 50 goals this year as a 17 year old, whereas 18 year old Picard in his draft year only scored 39. Mantha has a better release, better hands down low, and far superior hockey sense than Picard did.
For Pulock, from what you've said here, it seems like you've never seen him play. He has most of the tools to be a far above average defender in the NHL - including a terrific shot. Putting Morrissey ahead of him on your list is borderline crazy. Morrissey's skating is strong, his puck moving is good, but defensively he's a liability, and will require a ton of work just to be an NHL player. As one of the biggest Morgan Klimchuk supporters on these boards (even wrote a feature on him), putting him in the top-20 is not something I feel safe doing. I thought he had a great year, produced a lot more than I expected - but his upside is similar to Hartman, and he's far less a sure thing because he has to produce offensively to be in the lineup.
The logic just doesn't make sense on a lot of what you said. I get liking certain players more than others, but moving them ahead of guys who are clearly better now - and have higher upside - is an odd choice.