I feel individuals have a limited amount of energy to give in a day. That varies by person, by stage in life, your overall mood and mental health, plus how engaged you feel with the world in general. I don’t think there is anything wrong with needing more “downtime” than other people. And that is one aspect of “balance” that I feel gets overlooked. If you don’t have the downtime you need, it’s easy to burn out (at the extreme) or to become ineffective in what you do (more commonly). I love my job, but I’ve structured my life so I get an afternoon nap most days and I don’t want to give that up!
But in general, I think less about balance and more about variety.
Keeping your energy up and your mind engaged is more difficult if you only give yourself one or a few tasks. That’s my biggest concern with work (even work you love) coming to dominate your life. It doesn’t allow for cross-pollination of ideas and parts of your life feeding off the energy of the other parts. It’s a bit like how we’ve come to understand that biodiversity is important in nature and how cultural diversity is important in the workforce. If your mind is singularly focused on work tasks, I fear you are limiting yourself and lacking in personal diversity.
I think a lot about work, but I also spend a chunk of the day engaged in other interests: design, urban planning, European detective shows, my kids, the Raptors, the fallibility of the human mind, digital legacy, music, dumb memes, reducing extremism in all parts of society, dogs, Lego, napping, etc.
If people get joy and energy from singular focus, more power to them, but I’d urge giving thought to how downtime and diversity of thought and activity might benefit you in the long-run.