You shouldn't take CMC listed coins as legit though, they also go bust.
CMC listing shouldn't be deciding factor in judging quality of project, there isn't much in getting there really.
CMC only lists projects that have been registered on their site. I don't know if CMC will do an analysis first or not. But you are right that projects that have been listed on CMC can also be useless projects like LUNA. When LUNA crashed which made its price drop by 99% but you can see that Luna Classic is still listed on CMC. At least CMC can help you avoid scam projects. But some projects can be unlisted from the exchange or CMC.