It is truly possible to do negative DPS in Bloodtide Coast (relative to solo or just autoing on the worst mismatched gear with weapons at range).
Cannons do zero damage to the end boss (no spoilers) when the Corrupted Ice wall is down. I found this out the hard way while "soloing" the boss to 40%. I was wondering why it was taking so long, apparently the four people on cannons weren't doing any damage. I tested this by stopping all attacks on the boss. The four people on cannons did less than 0.1% over the span of a minute. I had to coax them off the cannons this way, because people are oblivious to whether they are doing any damage at all.
Of course the same people were trying to kill mobs instead of bringing wood to the lighthouse fire despite the event at the sidebar clearly stating the objective, so the level of attention people have is approaching zero in DRMs. That can be safely "carried" , so it isn't as large a problem.
I'm not sure if this is a game design issue or a player-made one. While it would have been better to disable the cannons completely when they do nothing, similar to in Siren's Reef fractal I would expect people would at least pay attention to whether they are doing damage.
(I had done all CMs for all DRMs already so I was just trying to be casual on necro, turned out it took more time than CMs.)