Wouldn't backfire work well?
I know what you mean about annoying, even playing the Hydra in the back would be touch and go as defense if they're doing that much damage.
Shields/ repair/ triage/ snipe - would maybe help get rid of Coral Wraith straight away.
Or SB with the taunt?
But you don't know if they are going to use full sneak. You can't take the risk placing Hydra especially if the rue is not mele mayhem
I hear what you say, I was really just throwing out suggestions!