I'll help get this ball rolling, as this looks like an interesting thread. I'm gonna use my favorite DD and my very first job: DRG! Yes, lolDRG, the DD that's rarely seen anymore. :|

Truth be told, DRG used to be an upper-tier DD for a while. Technically, in terms of damage, it still is. But comparative to the number of procs that other "main" jobs (NIN, WAR, MNK) get in Abyssea, it tends to be left out more often than not. Outside, it's not a bad job, but Drakesbane suffers against, for example, mobs like the T3s on the Jeuno/Zilart Voidwatch Path. I tell you, seeing a 300-400 damage Drakesbane really hurt, especially since spamming Wheeling Thrust for 600-800 was more effective. This is with Sole Sushi and my current WS set (See here), which has a fair amount of accuracy in it yet Drakes still misses a few important hits.

What I'd like to see is for DRG to truly become a top-tier DD again. One of its biggest damage-dealing capabilities is the ability to deal a lot of damage with weapon skills and attacks while being able to shed hate quite quickly. Super Jump, and now the hateless Soul/Spirit Jumps for your TP gaining are all ways of keeping hate off of you. You can also substitute Soul Jump for High Jump if you need a little extra enmity loss. DRG is also a fairly self-sufficient DD using a good Healing Breath set, especially with how survivable our wyvern has become lately (Though Pil still eats him in 2-3 TP moves!).

The problem with being a low-hate DD now is that it's easy to cap enmity for just about any melee job. You wouldn't be surprised if hate swings off of the tank onto you with a single hit and then right back on your tank's next move, and as a result the ability to shed hate isn't as vital because it's not hard to take hate off of the tank for any DD, not just DRG. It's good for your own survivability, but it really takes away from the original purpose of keeping hate solely on your tank(s). As a result DRG has lost its niche in a way as a DD who can do incredible damage without fear of peeling hate away from the tank at a bad time. We pretty much are unique now only through jumping for TP and we have a wyvern whose usefulness is questionable. Breaths are of limited use for Voidwatch because they like to stick with 1-2 weak elements (mine liked Flame Breath on Pil, for example, when it was Thunder Breath for proc), and Healing Breath is only good until your wyvern starts croaking from TP moves and your once-per-three-minutes Spirit Link isn't quite enough to keep them going.

I'm not really sure how to improve this, however, to make DRG more of a unique job. I'd like to see some ease on the breaths - for example, use a menu like Quick Draw where you select Smiting Breath -> Specific Breath rather than Smiting Breath and pray you get lucky - as well as some improvements like Healing Breath IV (which I heard was coming?). But more than those breaths I'd like to see the DRG's unique role come back in being a reduced-hate DD. What do you think are some ideas to offer this?