Here’s a suggestion. Maybe make the game a bit softer on newbies? Just a bit so it’s fair? Just so they stand a chance. Just so they can enjoy the game, get a feel for it, get hooked, before it goes full hardcore, balls to the wall, your mothers watching and is disappointed in you Spacelords? And increase the rewards for people playing mentor matches while you’re at it, give us a light at the end of the slog to look forward too. Who knows, maybe this would increase the player count to the level where MMR wpuld be relevant?
Overall I doubt new players enjoy getting their faces smashed continually. It’s not fun for me watching it either, watching the teams lives slowly evaporate into nothing as an unranked player sacrifices themselves to an Elite who then rampages the rest of the team.