I found a build that can do a minimum of 17k dps
(I can't possibly make it in-game because of the rng required, but I would love it if there were a sandbox mode to test it out and see what its real dps is)
It might have to do with the bone shard item getting multiplied by damage bonuses, but the build I'm referring to is cinderblock fish and snails (potential 2025% damage bonus).
(I haven't been able to even get close to an all level 3 run, though, so I think it might be balanced by the rng requirements)
Edit: just tested it; the bones are definitely benefiting from the snails' damage bonuses (when I killed the tentacles, the dps shot up to 85k)