"And this is why everyone needs a big slug of dollars in their respective reserves - to buy oil."
This petrodollar conspiracy is baffling.
Countries don't hold dollars solely to buy oil.
The oil and gas industry is only about 4.6% to 6.5% of the global economy.
Countries hold reserve currencies to manage the exchange rate of their currency. Petrodollar conspiracists would be well served by learning about foreign exchange reserves: https://en.wikipedia.org/wiki/Foreign-exchange_reserves
And in any case, only 65% of foreign currency reserves are in the USD.