There should be a way to have matchmaking refuse to partner with someone. Blocklists don't do it.

There is a player who I assume is tanking for some reason. In our last three 2v2 ladder games, he is intentionally losing (using gift card to an opponent, blockading another spot, and triple-tapping from the third) on T1. I don't know or care why he's doing this, but I shouldn't be forced to play with someone like this.

You can team up with a partner of your choice, no? Teaming up with random partners is bound to lead to undesirable pairings, which is also why the pool is so small.

It's a relatively large pool. And it's lots of fun playing with lots of random people. One potential teammate out of 50 shouldn't ruin it for everybody.

Sure, I like playing with some people better than others. But everyone is playable, and that's the fun. Except this guy, who tanks T1 no matter what.

I also think blocking should prevent the player you blocked being your teammate in QM/ladder/any team game. Maybe requesting that as a feature request could be more effective.
(Also I dont think it should be that hard for you to find a teammate, as like even without someone trolling it is more fun imo.)

Suppose that was implemented. What will stop people from blocking everyone except for the strongest possible teammates?

So give people a maximum number on their partner blocklist. There shouldn't be more than two or three that anyone does this for.