Shanahan? Not sure about that one. The dude was a PF winger who scored 50 goals and got 200 PIMs in a season. That's not Monahan's game, from what I've seen of it. If it was, along with his qualities as a pretty good two-way C, he'd be top ranked or close to it.
Anyway, although I am sceptical when people say, "draft BPA, never for need!" because I think BPA is such an elastic concept that can include preference based on position, I don't think you pass up on the top rated prospect on your draft list just because of his position. If Morin is the top player on Timmins' list at 25, then the Habs just take him.
I just don't think you make your draft list saying: forget defencemen, we have enough of those, let's get a nasty forward! In making your list of best players, I do think there's some room to say, for instance, that a potential top 4 D bruiser with a mean face might or might not be a better prospect than a potential top 6 F smasher with an angry face, all else being equal, but if your list ends with one ahead of the other, then you go with that player on draft day regardless of his position and your immediate roster need.
