Could quite easily believe that, anytime I've looked at it on Steam in the last few weeks there's been less than 1,000 people playing at peak times. Essentially that translates into; it's dead. I'd be very surprised if the people playing could get matched up for online/co-op with so few people & if you do you're probably going to get paired with someone on the other side of the world.
Compared to launch there was I believe as high as 35,000 I think I remember it seeing, currently, we're admittedly not in peak time as I write this, there's only 500.. to put that into perspective Arkham Knight currently has 800 playing & Arkham City has 500.