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?
I cannot give an answer, because the question is too vague. It depends. For example, if you want to trace a whale, then chances are, it's easier with coinjoins, because amounts are not hidden. In Monero, you don't even know when an output is being spent, therefore it's extremely unlikely you extract any information apart from the fact that you have 100 suspects.