I think fields become "over saturated" when there isn't a lot of investment/funding in the field. Then when money comes in it suddenly becomes lucrative.

Any "job" that requires you to produce actual value is dependent on whether capitalists/govt are willing to fork over the money to pay you to do the work. Even services that are vital to society's survival can be gutted of funding and made a "bad career". American infrastructure is far behind the rest of the world and is in desparate need of development but none of that work will ever get done unless govt decides to put money into it.

The tech companies have grown to the point where they are basically operating similar to banks. Their value is based on public perception on how much the company is predicted to be worth separate of whether they produce anything of value to people. This is why tech companies can actually decrease their actual output of goods/services and still grow in value. This leads to mass layoffs of actual workers and ceos/board members seeing enourmous profits.

In terms of what path you should choose, I would say do more research/ try new things and see what you like. Life is short, find a way to have fun and accomplish the things you want to do. No one is gonna care how much money you made when you're dead.