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?
Your graph is missing the more important factor: demand.
I'm guessing you weren't born into money, which is what most ultra wealthy people do. So failing that, you need to cultivate a skillset which includes doing something that other people want and are willing to pay for. And yes, that often means learning specialized, or dangerous skills. Take something like a high voltage electrician, they can make good moeny but they need a specific skillset, certifications, and fucking up can mean dying very quickly. Construction divers or underwater welders can earn good money as well. Though again, specific skillsets, certifications, and risks. On the less risky side, programmers can make good money, though that usually does require a lot of learning. IT and cybersecurity also fit this bill, though they do tend to follow your graph.
In short, businesses pay for people because they have a need for something to get done. No need, no money. You can be the most knowledgeable person in the world about flaking stone tools, and you are going to be struggling. Another route to income is starting your own business, but this has similar pitfalls. Start a business which people aren't interested in and you're going to flounder. Also, running a business does take it's own skillset, beyond the skillset involved in whatever the business's focus area is. Though, done right, you can focus on running the business and hire people to do the other stuff.
You are falling into a trap a lot of young, smart people do. You are assuming that knowledge and intelligence is what you need to succeed. It's not your fault, you've been fed that line for the last 12-ish years of your life by schools and society. It's bullshit. They do help, but knowing the right people, luck and the ability to socialize are more important. In short, go to business school and go into management. If that doesn't appeal to you (and that is perfectly valid) then you need to find and learn skills that businesses are willing to pay for. At the moment, that probably means a trade, like electrician or welder; or, a technical role such as engineering, IT or programming. If your interest is in the Humanities, sorry you're probably fucked.
Networking in university got me my first jobs and they were very good starting jobs.
I donβt mean you have to go out and be fake, but get involved in a bunch of stuff, and make sure to check if your department has any corporate relationships you can use.
Meeting people pays the best dividends in life.