What would be more private, let's pretend these are actual numbers of users - 10,000 CoinJoin users or 100 Monero users?
Those are rookie numbers. The Monero users are, by far, greater in number than Coinjoin users.
And no, the anonymity set of Bitcoin is not greater than Monero, just because it might have more users. The overwhelming majority keeps them on exchanges, under KYC, and from the rest, the majority of the coins are simply kept on a self-custodial wallet, without any privacy enhancements apart from coin control. A brief look at Bitcoin's current privacy options makes this clear.
I'm not debating for Bitcoin as more private simply because it has more users. I was merely thinking about the comparison from a theoretical perspective. The same question - If there are 10,000 CoinJoin users and then there are 100 Monero users, in theory would the users of Monero be easier to trace/identify and/or make less private?