WAR Zodiark Extreme is 200 behind GNB.
https://www.fflogs.com/zone/rankings...l&spec=Warrior
https://www.fflogs.com/zone/rankings...pec=Gunbreaker
WAR Hydaelyn Extreme is 100-300 behind GNB
https://www.fflogs.com/zone/rankings...l&spec=Warrior
https://www.fflogs.com/zone/rankings...pec=Gunbreaker
The list goes on. WAR will never out damage GNB unless it's a good WAR vs bad GNB. GNB is simply designed to do more damage. Just like WAR is designed to heal more.
Also nobody is saying DRK doesn't need work, however it's not in a desperate situation as people like you are implying. All it really needs is self sustain that rivals GNB and it'd be perfectly fine in all content. Anything else would be a sweet sweet much appreciated bonus.
Lastly how are simple balance points (heal more do less damage, vice versa, etc.) misleading? That just doesn't make any sense. If WAR did the most damage, healed the most, and had the most mitigation it would truly be broken. Any tank in that scenario would be broken. So it's common sense for every class to have pros and cons.