These guitar hero style alternative notations are a major problem IMO. It's extra problematic to advertise it as "learn music" when really it's giving you a crutch to avoid learning music.
I don't see the problem in an alternative notation if it's easier to read (I don't know if it is, I've never used the app).
But... learning to read music is an effectively insurmountable obstacle for many people who might otherwise enjoy playing music in a limited capacity, or in musical styles that don't make much use of reading. For this reason, I appreciate development of alternative notations. There is already an extensive literature of written music for guitar and electric bass, that uses "tabulature," a notation based on numerically identifying finger positions on the instrument. Percussion notation is a kind of tabulature.
The problem with alternative notation is that standard notation represents a symbiosis between composers and performers. Composers know that if they use a particular notation system, then there will be plenty of people who are capable of reading it. Performers know that if they learn standard notation, then they can tap into extensive literature and performing opportunities. Nothing like that exists for any alternative notation. Even with guitar tabulature, very few composers know how to write it unless they're guitarists, and nobody can "sight read" it, so it's use is limited to learning material that will be performed from memory.
Granted, I've just made a lot of generalizations, but they hold pretty well, most of the time.
I look forward to the day when I can don a pair of high-tech glasses, look at something written in standard musical notation, and have it "transnotated" on the fly to something easier to read!
But I don't know how much of the problem is our notation, versus the fact that learning to read is hard. It's almost like becoming fluent in a foreign language, which we know gets harder as we get older. I started learning to read music when I was 6. I don't know what it's like to learn reading as an adult.
I suspect that that is part of how it is with our standard musical notation. The people who already know it have no interest in learning another system, even if it were demonstrably "better" (for some definition of better).
It is my opinion that our current system expresses a lot of irreducible complexity, but also has a lot of incidental complexity due to quirks of history. Accidental marks, in particular, strike me as making a backwards-compatible change that is easier for the people already locked-in to the system, but has made it more difficult for learners in the centuries since.
There's a really simple change that would roughly halve (!) the effort to learn to play music written with a grand staff. Right now, it is, from the bottom up, composed of a bass staff, one ledger line, followed by a treble staff. Simply changing it for a treble staff, two ledger lines, and another treble staff, would make it so much easier for people learning to read the music.
Going one step further, if every octave looked the same -- why should half the Cs be on lines, and half on spaces? -- that would make it far easier to learn the notation.
(And don't get me started on the timing system!)
I heard of a fluent sheet reading kid who was introduced to Klavarskribo. Apparently after 45 minutes of learning, he (she?) was able play pieces he'd never played before, just because the incidental complexity was reduced.
Perhaps another thing that saves standard notation from itself is that most of the time, we're not actually reading all of the notes. In my case, working within a particular musical genre (jazz), my brain knows what the next notes will be, even if I'm not looking at the page. And when working up a classical piece, you've memorized it after a couple weeks, and the chart is just a place to annotate special things like fingerings and problem areas.
There was an article about a famous piano concerto, where someone discovered a mistake in the accepted transcription, and nobody even knew about it because everybody just instinctively played the right note.
I'd love to see an application that could capture audio from an instrument and act as a real-time theory aid/teacher. For example:
* the note you are playing is this
* the notes you've just played in sequence belong to these scales. here are possibilities for next notes
* try these chords
* the chord you've just played is comprised of these notes
* the next chord in the scale could be this
* popular songs with these chords or in this scale areI say the more tools the better. People will outgrow their instrument fairly quickly if it's too limiting and then just move on to something new.
I am a noise musician, among other things. It's an entire career. And whether music is about conveying emotion ... I don't know if that covers all the edge cases.
My favorite definition of music is "sound arranged over time."
However, I totally agree with what you are getting at. Learning music is really about learning conventions and common language, which allow you to communicate emotions and mental states, especially at the beginning.