I've been playing long enough I can usually pick up a melody by ear, but sometimes it is transposed. Even without a key signature the videos help knowing what key it's in. Timing and expression are in the actual audio, so for me it's not needed in the display. I'm trying to play it how I hear it, not how I see it.
I also have an ok ear for melody and given a bit of time can usually come up with some sort of harmonisation so I get learning by ear.
But for me that process is about listening to the music or replaying it mentally.
I don't get what this seemingly popular falling note/guitar hero style display brings?
You mention that you use it to tell the scales used in a piece? To me, the "falling note" representation is a poor and indirect way to communicate that information.
For me there is nothing indirect about it. The falling notes point directly at which key on the piano to press. I can hear it's a I, IV, V, VI progression, but I might not recognize it's in the key of A#. With the falling notes, I see the first chord is A#. I might get that from sheet music too, but it's a lot harder to decipher.
