Aang, the only exception ever, made a new technique and had already mastered 35 tiers. They let him skip one. Making a brand new technique, although notable, The statement, officially, is "and/or" because it was never clarified if the creation of a technique is a sure-fire skip to Airbending Master. In any case, it's not going to alter the situation too much here.

Almost every character I see tries to take on the title of master, and not one has actually deserved it. The title is meant to inspire reverence for a reason. I'm not going to hand it out to any of any bending class easily.