Earlier quoted context omitted.
Economy is closer to a zero-sum game, after all theres limited resources in a period of time. We cannot be all rich because we cannot all own the capital, if we did, who does the work? To invest you need workers, to produce you need consumers, to rent you need renter, etc. Then the rich class exist because theres a poor class, a zero-sum game.
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a) it's impossible for everyone to be a (successful) businessman: somebody has to be an employee and do the actual work, y'know?
b) to be "actually rich" -- which is not just "being on the level of personally comfortable standard of living", it's more of "having certain level of personal influence" -- you have to own a share in a commercial enterprise and get the dividends from it; rare exceptions like a prominent lawyer or a genius surgeon notwithstanding.
These two are mostly empirical observations, and you can frame it very differently depending on your liking; the "exploitation of the worker class" is only one such frame, there are many other.