So, I tried changing region and it makes a massive difference. The "Europe" chats are more or less all dead while the NA ones are very active.
The matchmaking is clearly affected by this setting as well, as I can now join a random fissure mission and actually get people to join me.
The lag is worse, predictably, but at least I can trade and join radshares.
I really want to acquire Ivara prime as she is by far my favorite frame. I can't really find radshares for her relics though, but I will try again later this weekend.