I was having a hard time with the new proficiency mechanic and after some reflection, I realized that my problem wasn't really with the mechanic itself, but with the word "Legendary". The difference between +2 and a +3 seems too pedestrian to justify a "Legendary" status. "Legendary" should be fairly unattainable to mere mortals.
How about something like Trained > Advanced > Expert > Master? Or just a Proficiency value? (e.g. Prof: +2)