Bungie has painted themselves into a corner with Ghorn melting bosses. They can't nerf it, and they can't increase the synth timers because that would screw ever other weapon (and wouldn't stop the ghorn spam; just slow it down). All I can think of is what they did with Crota, where the only weapon that could damage him is the sword. Maybe they need to use that sort of idea more. Drop shields with regular weapons, and use things in the environment to kill the boss (exploding things, possibly geometry things like destroying a bridge he crosses while he's on it (a la Bowser), etc.