Jack Johnson isn't the first freshman defenceman to rip up the NCAA. It happens quite often. So to use that as your judgement is flawed reasoning. You could say that about several other players that never went on to do anything at all. Until either Johnson has done something at the NHL level it is all purely speculation and personal preference, nothing more.
As for the person that said Brendl has more upside than Staal, I would have to disagree there. Brendl may have more natural talent, but there is a lot more to upside than natural talent. How about brains, vision, heart, etc, etc. All things that Brendl does not have, hence the reason why he isn't an NHL regular.