It may help to think of your life as “epochs” or “seasons”. Sometimes you’re in a work period, or in a startup epoch. Another time you’re in a travelling season. It’s easier to split your interests over time than to parallelise in the present. The season idea can be greatly reassuring - “oh, I’m not doing enough music now, but that’s because I’m in a work period. Focus on work, do that, that’s enough. Spare time - rest, recuperate, so I can do better work tomorrow.”
I think there are certainly some benefits of focusing on one thing or epoch, but I do wonder if most of my energy going toward one thing would make me no longer enjoy that particular thing. Regardless, I like the concept and how it perhaps pertains to people's continuous change/growth.