I don't have the energy to code on private projects for eight hours after eight hours of coding at work (besides occasionally enjoying not sitting in front of a monitor...). But every once in a while it bites me to blow 10 hours of tinkering on some strange useless problem, like simulating Logic-Gates with basic arithmetic.
> No dentist gets told he gotta setup a practice in his garden shed to practice pulling teeth
This is a weird argument to me, the medical field has an even more unhealthy work/life balance than our field. They absolutely "practice at home" (obviously not through home surgery, but reading and so). Dentists have an easier time than most other medical professions, but every dentist I've met regardless had extremely good work ethic and frequently obsessed over his work.
You can absolutely work 40hrs a week and be a good engineer business-wise. However, most people who are remembered for their contributions to a field (and weren't just in the right place at the right time) dedicated a large part of their life to it. That includes writers, poets, musicians, doctors, anything.. to quote old Onion videos: are tests biased against students who just don't give a shit?
It is very common for professional athletes and for anyone who wants to live off their art (painters, musicians, writers, etc). Most academic types I know are like that too.
There are plenty of programming jobs where 40hs a week is enough and you get paid a good salary.
Now, if you want to join a FAANG, that's a different story. But no one wins a Grammy by playing exclusively in weddings either.