Even had they gone 82-0 (which is more than 4x more difficult than 16-0 is in football) but lost in the finals, their feat would be forever tainted and much less impressive.
You're having trouble following along at home. Perhaps we can be more productive if we establish a point on which we agree:
From a sports perspective, is the legacy of the 2007 Pats tainted because they did not win it all? Yes? Good, let's try another:
Is 16-0, i.e., a perfect season, different in kind than 15-1, a non-perfect season? Yes.
Is a PF70, a perfect coin, different in kind than a PF69, a non-perfect coin? [insert answer here]