I know what you mean, but I think Thrun basically stepped in as a (mostly) fully formed player in terms of what he is and what he will be. I was happy to vote him 6th because of this--and because players of his ilk often get underrated--but there's also likely a ceiling to his level as an NHL player (I feel like a responsible, fairly low-scoring 2nd pairing and PK guy is about right).
Someone like Bordeleau will have his flashes and probably has a higher upside, but that upside is harder to reach than Thrun's, and then the question is, if he doesn't reach it, can he be a good bottom six player? Whereas Thrun has the safer floor to go with the lower ceiling. It really speaks to why even when trying to be fair and logical, ranking prospects is inherently difficult and subjective.