everyone buying BTC become rich
everyone cannot become rich.In a debt based fiat money system, it is a zero sum game, your saving comes from another people's debt, so your conclusion is correct
But in a debt free money system like bitcoin, it is totally possible that everyone are rich, since every BTC existed are not a kind of loan, the electricity, time and R&D cost of the mining equipment has all been paid and contains in each BTC, it is debt free and have value coined in, everyone can get BTC with their product/service without incur a debt somewhere else in the society
Ignore the USD exchange rate, that partly depends on the USD supply by FED, do not really represent the real value of BTC, market is discovering that value now