Not so sure who if Coinbase has more users than Binance but even if they have, I think Binance will still win in terms of staking platform since the majority of their users is knowledgable in cryptocurrency and for sure they have an idea how staking works compare to the users of Coinbase.
I must admit that coinbase really successful when it comes to advertising and it seems their target audiences are those people who want to try crypto. Meanwhile, Binance's users consist of somehow experienced users in term of crypto whether it's trading or staking though. I agree with you that binance users have more potential for staking their assets in the exchange. But, if coinbase could successfully elaborate staking to their users, the potential they may get out of it couldn't be underestimated.