You are almost convincing me to change my stance Lydian, but only almost. A lot of good points, but still lacking a little when it comes to explaining how practicing an instrument does or does not train your ear. I think it does.
In that case I will most likely not be the one to persuade you. I can only speak from my own experience as a multi-instrumentalist. I consider my ears to be my greatest strength. I would not however attribute that strength to playing instruments. When I first started playing guitar (12 years old) my ears were absolute garbage. Unlike Zau, I was not born with any type of perfect pitch. What I did realize though was that only being able to play music if I had the tabs for it became HIGHLY limiting. Not only were the tabs on ultimate guitar often incorrect but they weren't always available either.
Therefore I made a conscious decision to stop using them very early on in my playing. I downloaded transcription software to slow songs down sometimes as slow as 25% to be able to learn the notes by ear. I had no real concept of music theory and didn't even know how to subdivide notes or count beats. I had to force myself to learn music by ear, improvise over backing tracks, transcribe music in Sibelius, and only then was I able to develop my ears.
Then came in music theory which essentially skyrocketed my ears to levels I could never imagine. Suddenly I was able to perceive music in scales, arpeggios, melodies, harmonies, chord progressions, modes, intervals, keys, tonal centers, and subdivisions. Learning music theory enabled me to hear music in patterns, numbers, and terms.
Which is why this...
No amount of music theory is going to help you in the first place if you can't HEAR what you're doing.
annoys the hell out of me.
Someone like Zau who has perfect pitch would not be able to relate to beginners having shit ears in the first place because he was simply born with it.
. Since you brought it up, the way I did it is that I was born with good ears...