I don’t think it’s possible to be happy when working 80+ hours a week

I think there's a certain element of "do what you love and you'll never work a day in your life" in this.

If you're really deeply invested in a project and doing it brings you joy, then you very well might find yourself investing every waking moment working on it.

But that's not a "job", that's a "passion". You typically don't get to pursue your passions unless you already have a big passive income or a sugar daddy willing to cover your expenses.