The downside to graveyard zerg is you at least have to have
1 competent player to keep the boss going if your whole group sucks the one good player shouldn't have to be punished with going against the boss solo because he is doing everything right.
For example I actually soloed half of the 3rd golem in sorrows embrace story while everyone else just stood there and waited for me to die. I dodged wrong and a poison barrage got me
.
The second downside to graveyard zerging is the repair cost, if you are constantly zerging I hope you like wasting your money.