Can we please, Please, PLEASE get away from the 25+ year-old "Kill hordes of trash mobs before getting to the final boss fight" trope? Maybe, just maybe, the actual story instance can have it for the "flavor", but once you hit the repeatables, then no. If the devs are concerned about grinding them multiple times in a certain time limit, put a cooldown on player's accounts being able to do the mission, of 15 or 30 minutes since the last completion on that exact mission. Maybe a similar "attunement" like in Silverwastes only account wide.