But if a coordinator doesn't accumulate enough liquidity, then like you posted, it would be less secure, inefficient, and therefore a less effective way to CoinJoin outputs.
Yes, bigger coinjoins are more efficient than smaller coinjoins.
Plus, I know the liquidity pool is supposed to be made of user inputs, but if not many users actually want to use the coordinator, then there should probably be a bootstrapping process during the start, no?
The coordinator can participate in their own coinjoins of course, but they still only count as 1 user.