I think those of us who have burned out in a profession need to be careful when giving advice to the next generation. I got burned out in aerospace engineering, but I still encourage young people to explore their interest in the field and help connect them with opportunities when I can. My burn out was some mixture of a "me" problem and the normal life cycle of a motivated individual in corporate America. Telling a young person not to pursue it because I got burned out would feel akin to an elderly person telling me not to get old because they got cancer. Yes, it sucks. It is also just part of the journey, to some extent, and there are burned out people from every single profession. I think the best we can do is be honest about pros and cons, as objectively as we can, while avoiding blanket do or don't statements.
Regarding humans flying airplanes, I agree it's hard to picture two pilots per airliner 50 years from now. Clearly things move towards more and more automation. In this age of AI, it is also hard to picture what any traditionally high-paying occupation will look like 50 years from now. The bots seem to have everything in their targets. They are even solving exceptionally hard math problems (see Millennium Prize) So, if you are passionate about flying airplanes in the traditional sense, I say do it NOW, while it's still on the menu, and enjoy the ride. But don't be naive. Be frugal and acknowledge that you will have to reinvent yourself in the future. That's advice that holds for young people entering most professions today, not just aviation.
Best of luck to the OP's son as he sorts things out. "Simple it's not, I'm afraid you will find, for a mind maker-upper to make up his mind" - Dr. Seuss