Weight alone is less important Brian. To oversimplify a bit, a 12 pounder flying on a 1200 sq inch wing will fly superbly given the right amount and type of power...In contrast, a 10 1/2 pounder flying on an 800 sq inch wing, less so.

There are several other key factors but that's the basic idea

I think Mastertech meant that given a common design and all else being equal, the 12 pounder will not fly as well as the 10 1/2 pounder...he's correct on that! But I could be wrong in my assessment of Mastertech's actual meaning