I'm curious, how does this approach fare with classical pieces where learning by sheet is the norm? The melody and chord progression is not hard to for a lot pf pieces (e.g. pop and jazz if you have a trained ear for complex chords), but learning Listz's Un Sospiro by ear is going to be really hard no?

I learned that piece by its 6 page sheet then memorized it, would be amazing if that could have been done by ear, if possible.