The positional value should be factored into the evaluation, because it has an impact on the ice. But, that's a weighted issue. Although, a lot of center prospects aren't locks to be centers, and eventually end on the wing to be effective NHLers.
I don't think it's easy to predict your team's needs in a few years. People bust, disappoint or are traded in packages. Very few prospects outside the top 3 are sure things.
In 2011 the Leafs had a need for a center at 5, and had a promising D breaking through in Gardiner, a recent 1st rounder in Stuard Percy, plus well-regarded but overrated defenders (Dion and Franson). I'm sure as hell glad we didn't reach for the next potential center in Grigorenko and left that draft with Morgan Rielly.