Damage meters is clearly necessary, if you want competetive OR progressive PVE/PVP. There is actually no way to calculate either if your spec is right or if you're using the right compination for the time being, a damage meter would fix this.
+ It would add a fun aspect of raiding, instead of just clearing the same instance over and over again. This would buy some time for the Ops developers to develop more content due to the lackage of the current one.
+ would paint out the one who's dragging the group/ops down, if you're wiping because of a player, you want to know that, not waste time trying out different tricks and tactics.