The sort of well-to-do 40+ lawyer you describe is really only something found at "biglaw" firms, and not only that, but people at biglaw firms who have managed to make partner. Getting hired into biglaw is like getting hired into big tech from CS school, but less predictable because it's almost universally based on law school rank after your first year. And law school rank is almost universally dependent upon exam grades. In law school, your grade for a class for the entire semester is dependent on one exam; mine often had somewhere around 4 questions. You can know the material back and front objectively, but if you have not managed to divine how the prof wants their questions answered, you will score poorly.

Everyone goes into law school thinking they will be the one to get high grades, but in my experience, working hard was not well correlated with good grades. Even if you work harder than anyone else, it still somewhat comes down to a coin flip. This can be so frustrating, I cannot even begin to describe it.

Even if you then make it into biglaw (a low percentage), you then need to make partner (an extremely low percentage). This is far more about a) office politics, b) connections, and c) your ability to "rain make" by bringing in big new clients; than about your skill as a practitioner of law.

I would also caution against looking at numbers like salary in isolation. Law is full of unhappy rich people. 36% of the profession suffer from alcohol use disorders, compared to ~12% of the general population. Nearly half experience depression at some point (compared to 15% in the general population, in the stat I was able to locate). It's not a happy field.