So I'm 20 and I've started looking at the salaries of jobs/careers, and this is the impression I've gotten. Like that you could spend years cramming a ton of knowledge about a very niche field, and still only get 2-3x what a run-of-the-mill job makes. Is this true? If yes then I guess this route to wealth would only make sense (due to the diminishing returns) if the topic truly spoke to you, right? Are there alternative career paths to good pay than being really good at something really specific?
You're out of touch with reality with this idealist conception of wages as a result of knowledge. The value of labor is the cost of its reproduction. Capitalists pay workers exactly as much as they need to for them to turn up again the next morning. Knowledge does not directly factor into their calculation. Don't expect to be rewarded for the work you put into your education - the system isn't fair and doesn't work like that.
Instead, wages are the result of a collective power struggle between labor and capital. High wages occur either when labor is strong and capital weak or when you betray other workers and aid capital in their exploration.
Now expert knowledge is one of many things that might help by increasing bargaining power in the struggle with capital, but it's neither necessary nor sufficient. For example an automotive engineer might have just as much knowledge as a chemical engineer, but where I live, chemistry earns you about 50% more, because the chemistry union is stronger.
So union power, strikes and social movements are a big factor. Others are location, the average rent, international competition, the reserve army of labor. At any specific time, the boom and bust cycle of periodic crisis strongly effects wages.
The organic composition of capital plays an indirect role: If the degree of automation suddenly rises, this will lower workers bargaining power short term and lower profits long term which increases pressure on wages.
So if you want a career with stable, high wages but don't want to help exploit others, look for sectors with a long-term chance of a strong bargaining position for labor.