I think the average Coinbase user also wears Binance. I myself use a lot of exchanges, because we can compare prices in each exchange. So if Coinbase has 30 million users, then Binance is likely to be more than 30 million.
I think comparing the two exchanges site seems right to me because the exchange has a different platform, rules, and regulations. Coinbase rules are to have legitimate users which make it impossible fake users to use the exchange site while most of the exchange site out there seems not to be bothered about such cases. however, coinbase is a billionaire company and to me, it will always be the exchange that have more users.