I agree with your teacher that the learning ratio can dramatically increase as a greater percentage of the new piece should require skills you already have, and challenges you know how to address.
This assumes that you choose repertoire and develop skills in a systematic way. If, on the other hand, you jump from a level three piece which took you three months to learn, to a level 10 piece, you lose the advantage of cumulative skill and problem solving development. .... and see no change in the learning ratio. ... you have a high percentage which is problematic and will take you very long to learn.
It is the best reason I can think of to be disciplined; to continually struggle over a large percentage of the score is not something I find enjoyable. There are many pieces of repertoire I want to play, but if my teacher’s advice is ‘wait six months’ or ‘do this first’, then I delay gratification knowing it will be easier (and better) later.
Hope this makes sense. I’d be very interested to know the context of your teacher’s comment, as from your previous posts, the order you learn music is not progressive: you learn Waldenstein, but have problems with Pathetique Mvt 1 or Chopin fioritura. Is your teacher trying to get you to postpone repertoire ‘until later’?