I mean, given enough time, just a mere salary man can become a millionaire (and with more time, a multi-millionaire) only by keeping their spending low
Technically true, if they are a highly skilled worker that’s in low supply
stashing the rest of their net salary into index funds
Index funds usually invest in other firms, where profits (read: appropriated surplus value of workers) is distributed among stakeholders.
Billionaires (and “multihundredmillionaires”) are a completely different group of people though, and no normal person is able to amass such wealth without a shit-ton of luck and most probably some abuse as well an economy that is organized in such a way, where no matter you work you’re at the mercy of the firms owners and their managment, where your surplus value gets appropriated and where refusing to participate in such system lands you on the street because you can’t pay rent.