If you're in a place with ethanol in the gas as an octane booster you're done right there.
Ethanol is fantastic at removing deposits. So much so when it was phased in 20 years tons of engines that had been running on non-ethanol blends had tons of trouble with deposits breaking loose and causing issues, especially anything with a carburetor that had built up deposits. The Ethanol broke down the deposits and then they'd get lodged in jets.
Modern engines seem way better at not building up deposits like you said, but things like Direct Injection also didn't become common (at least in the US) till Ethanol was also present.
Ethanol is fantastic at removing deposits. So much so when it was phased in 20 years tons of engines that had been running on non-ethanol blends had tons of trouble with deposits breaking loose and causing issues, especially anything with a carburetor that had built up deposits. The Ethanol broke down the deposits and then they'd get lodged in jets.
Modern engines seem way better at not building up deposits like you said, but things like Direct Injection also didn't become common (at least in the US) till Ethanol was also present.