In many ways I agree with your opening sentence---maybe I shouldn't have written "fun". I think I was trying to get at something more like that the experience of learning itself is itself a good thing (even if it's not fun, even if it's suffering, even if it's hard) and I think mechanical and stoic recipes to optimize the process fail to adequately appreciate that fact.

The best part of learning piano isn't getting good at piano---it's learning piano. And sure there are some things we have to learn that we aren't that interested in learning, but I think even those things have the capacity to be worthwhile experiences if properly framed.

I think applying the word "efficient" to this area is suggestive of urgency and greater purpose---I don't buy into either.