While the idea of a global mute function would be really nice (or just an in-game mute), being able to prevent people from matching with/against you has the potential for abuse.
IIRC, a good example of this is from a while back in 'Overwatch', where they had this exact feature for pretty much the exact same reason (prevent from matching with offensive players). The thing is, people would just block very skilled players so they wouldn't need to play against them. As a result, in some regions with very low numbers of high-skill players, certain players simply wouldn't find matches anymore - not because they were offensive, but simply because everyone 'blocked' them from being exceedingly skilled.
Regardless, I doubt we're ever going to get any match-making changes, regardless of how small they are. That would require server/code changes, and I don't think there are any staff with those skills on CoH2 anymore.
Hopefully (if its ever made) CoH3 will have more modern online functions (mute, more restricted MM ranges, ready-checks, leaver penalties, in-game reporting, etc.).
IIRC there's 2 different features.
Blocking communication and avoiding as "TEAMMATE". The avoid as teammate is limited and should work for like a week or something and it doesn't avoid facing them on the same game.