Learning just about any complex human activity results in obvious sustained improvements, for someone who cares and puts sustained effort into deliberate practice. If we leave out math and reading, we still have: woodcarving, dance, painting, rock climbing, gymnastics, sketching, football/soccer, cooking, chess, pottery, poker, speaking any foreign language, computer programming, graphic design, designing and building electronic gadgets, basket weaving, karate, public speaking, embroidery, juggling, mechanical engineering, and on and on for as long a list as you want...

I’ll agree, however, that music is an essential part of human cultural heritage, and every person should be given the chance to learn to play an instrument. Just as every person should at least a little bit learn how to cook, and to sing, and to dance, and to juggle, and to sew, and to program computers, and to write mathematical proofs, and to build wooden furniture, etc...

I think the great-grandparent poster was talking about something different though. Not teaching a child to play an instrument for a year or two to delight in music’s intrinsic value and then optionally continuing it if the child expresses interest, but ramming rigorous lessons down a child’s throat, forcing the child to spend years in training that he or she thinks is boring or a waste of time.