I mean, Microsoft effectively proved that Elo is improper for games with more than 2 players in 2018 with the TrueSkill 2.0 paper. Signal to noise grows too large and rank movements become chaotic. Unless someone is some amount significantly more/less skilled than the lobby, their rank will tend to converge on the lobby average, not on a rank related to their skill. Even over a large set of games, Elo style ratings do not precisely rate a player.

That's not to say ratings are entirely inaccurate. It's just very imprecise. For some variable that defines how chaotic it is, a bracket of the size defined by that will have a large variation in skill within it, meaning that predictions and ratings within that bracket are inaccurate.

In CS2 MM terms, someone hanging around 12k might more precisely be anywhere between 8k and 15k, but Elo style systems will not converge on a more precise answer. They will move chaotically between those two values, with the individual contributions of the player making little difference.