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.
My response to this is to mention how Xbox Live worked back in the early days of the Xbox 360, which had the Account Reputation System which basically was something similar but worked across multiple games that supported it.
Very skilled players or sweatys were being blocked and reported by a lot of unskilled players or non-sweatys, and because of that their Xbox account reputation was low. This caused very skilled players to have difficulty finding a match in matchmaking games, in some cases still searching for other players for more than two or three hours. Back then blocking a player blocked both their ability to message/invite/etc you as well as blocking them from being able to match with you in online games. The Xbox 360 had a monumental playerbase, especially in games like Halo 3 or Call of Duty Modern Warfare. Thats why it can still remain a problem. While Helldivers 2 is a PvE cooperative game, there is no reason that skilled players or meta players need to necessarily be so severely punished for playing the game in the way they like to play.
Its an issue where you basically have to create Competitve and Casual queues, and hide them from the players and automatically put them into the right queue based on the way they play the game for a few qualifying matches. The issue with this approach is if a player is inconsistent, or if an account is shared with multiple people, or if a player is a rare case of being a bit in both categories I mentioned previously.