If a fight has a rear cone attack it's just a matter of learning when it's safe to hit Impulse Drive. Disembowel and CT have no requirement. A Rear cone is also a very good opportunity to refresh Heavy Thrust. MNKs don't lose their combo if they aren't in position but they do lose DPS by not receiving the flank/rear bonus. If it's a radial AoE that is larger than melee range that's just a reason to properly manage Spineshatter and Dragonfire Dive. You can be back in swinging while the MNK and NIN are still running back into melee range. Basically a DRG may not be the melee DPS that can walk into a fight blind and manage their output, but they have all the tools to keep up once they know the mechanics and timing.