Regarding your point on not being able to be matched up against blocked players:

This is not healthy for a game with matchmaking to allow players direct control over its matching system like this. In a PvP game this would especially be a problem, but it has problems in PvE games as well. In this situation, meta players would just block other non-meta players, effectively lowering the matching pool to two different queues in a single large pool. In this scenario, it would be more efficient for the matchmaking system to just have two separated queues, which brings me to the next point.

I would argue the opposite. Vermintide 2 employs this exact thing and it’s been working pretty well - it actually does punish people who get blocked a lot by other people, and if you’re being blocked by a ton of people, there’s probably more than just “skill issue” and “you’re not running meta” going on. You do get sweaty people who block non-sweaty people, yeah, but it’s not hampering the community of the game in the slightest - and that game is waaaaaay smaller in size than something like Helldivers where you can get blocked by a ton of people and still play with other people due to the sheer size of the playerbase.