Coinmarketcap makes a ranking which is based on their marketcap

Which is imperfect and can be gamed by entities like riple or shitcoins that have the majority of their suply controled by two or three individuals.

they don't claim to be a rating site or anything

They don't have to claim anything, most people will take a glance and will form their opinion based on that inaccurate(coinmarketcap) list.

In investments (and not just in crypto) one of the most important things is to make your own research about projects, not to let others rate them, especially not if they come from sources which are most probably not going to make a fair rating.

This rating is a tool that can save you a lot of time in your research and was much needed, I'm not saying it's 100% accurate but it is the best tool we have so far. A tool to end hyped shitcoins and give us some baseline to start our research from, we are in a better position with it than without it.

I would have my reservations if there were some unrealistic ratings in that list but this is not the case, all rating are prety fair imo.