It's possible to take out the turrets pretty easily with eldritch blasts from outside; you won't get them all but once inside you just have to avoid the firing arcs of any you left (or polish off the last of them). I agree with the OP that it's one of the weaker boss fights as it can be either way too difficult, or way too easy. Plus you can farm the grenade launchers for lobbing grenades at Gortash to make the fight even easier.
