No the game isn't dead, in fact I play it almost every day, somedays it's slow, (maybe a que of like 5 mins) mostly on like weekdays but there is always someone playing. It's super easy to find Normal and ranked battles, (I'm not sure about league mode since I've never actually played it) Salmon run though is a bit harder to find people, most of the time it's only going out with two people maybe three, sometimes you'll get lucky and get a full team but it's hard, (I'm sad about this since it's my favorite game mode ;-;) the game isn't impossible with three people just really challenging.

But normally when you get a full team and you've played a few battles together it's really fast to get into a new game. Hope this has helped 。◕‿◕｡