Agree to disagree, I guess.  A team with a 6 seed means they're expected to lose in the Sweet 16.  Any team getting further than that is by definition overachieving and each successive win is harder than the last.  It's very difficult for seeds numbered higher than 3 (or maybe 4) to win national titles, which is why it happens so rarely.  Seeds higher than that reach the Elite Eight or Sweet 16 fairly frequently and then run out of luck.  That's why I don't consider them national title contenders.  The seed definitely matters, because it's indicative of their resumé.  National title contenders (barring bad luck with injuries, etc.) don't get 6 seeds.  If they play their way into the final weekend, they've turned themselves into national title contenders, regardless of seed.