I understand what you're saying, but I think ultimately the phrase 'work-life balance' is just shorthand for "I'm spending too much time at work and its disrupting the other parts of my life that are also important to me but that I've been neglecting".
If I tell people that my work-life balance in my current role is good, they instantly understand that I'm able to spend time on a range of things that are important to me (friends, family, hobbies, sleep, etc) but if I tell people that a previous role had a terrible work-life balance, they instantly understand I wasn't happy with the hours I was spending on work.
You can totally argue that both of those scenarios are just good-life and bad-life, but the phrase 'work-life balance' is efficient for these descriptions and doesn't require additional explanation.