I hate to be that guy but this is the only way SE will ever listen, by spamming forums about the job. Dark Knight has had too many outstanding issues that are more glaring than the other tanks. While all jobs have some gameplay issues, Dark is one of the most apparent jobs riddled with issues.
1. LD sucks. Its not 20seconds, its at most 11s. 1s from the time you die + 9s~ to get fully healed. People die all the time to this ability and its usually not their fault. Why do we get punished for doing the correct thing? Why do we get punished for doing something the other tanks get to do with no repercussion.
2. BW sucks. Its literally not 10s its like 9.5 seconds. Not sure how devs have disregarded this for so long just because JP has better ping. Its stupid, obnoxious, and barely relates to skill. This is the incorrect way of introducing higher skillcap. Ive literally had IRL friends tell me they have no issues hitting 5 gcds and then I check in Xivanalysis to confirm that they missed over 7 gcds in BW.
3. Self-Sustain is far far worse than the other tanks. GNB has two auroras + brutal shell on 2nd gcd + HoC. Their sustain is simply better because their mitigation is also better. Warrior I dont even have to explain. PLD can basically fully heal themselves with clemency/holy spirit even if clemency should never be used ideally.
4. TBN while the math checks out to be approximately equal in mitigation to other tanks, the other tank cooldowns they got/got upgraded are significantly better due to having no downsides/no punishing features. Make TBN 25s and no mana and its fine.
I dont really care about the other issues the job has because these are the most obnoxious things that need addressing.