My parents put me in piano lessons when I was very young. I remember going to my very first lesson with my Golden Books Songbook in tow, keen to learn how to play all of the songs on the first day. The disappointment upon discovering that I would not be able to play any of them right away was sharp but short-lived.
After a few years of diligent practicing (thanks, Mom!), I was actually able to play some interesting music. But I also had to play scales and do theory. Not the most fun.
But I don't think it's always the fun that is the most important. The fun IS important—don't get me wrong. The fun songs are the things that keep kids coming back to the keyboard day after day, week after week. But I recall having the most thinking time, the most bored time, while practicing my scales. Or writing in the counting. Or improving my technique.
There are tons of studies that elaborate, scientifically, why music is important to both developing and aging brains (see below for links!). But personally, I know that those years of boredom playing scales, or excitement working on cool rhythms or chords, or those moments of satisfaction when I finally memorized a difficult piece, are what really shaped me as a person. For myself, the self discipline and patience required to develop proficiency at the piano have been skills that have helped me in all other areas of my life.