Let's just look at it DPS wise, because otherwise DRG will get blown away by MNK and NIN. I agree that dummy =/= raid DPS, but it's certainly got its merits. You actually are hitting a boss with all positionals T10-13 large chunks of the fights, larger than 80% of the fights are training dummy for melee. Mechanics are usually once every 20s or so, otherwise you just smack the boss.
T10 - occasional charge (if not the victim of charge, minimal difference). Adds benefit those who can multi-DoT stronger and can start their debuffs on the enemy with less loss. Final phase, outside of tether smacking and avoiding overlapping Heat Lightning it's pretty training dummy.
T11 - occasional missed positional on the boss due to Nerve Cloud and in/out mechanic. Only final phase is a true positional difference, and possibly the biggest time in T10-13 where it's not training dummy DPS (where DRG can get hurt the most due to their reliance on positionals).
T12 - Blackfires force momentary flanking. Otherwise just dummy. Add phase is just dummy for melee except you attack new enemies constantly. Final phase, no strategy should involve melee in fountains, just training dummy except for the occasional dodging of phoenix charges.
T13 - Megaflare can force rear positioning once a minute, Earth Shaker can force downtime. Otherwise it's just pure dummy 90% of the fight outside of the add phase where you restart your rotations constantly.
These new fights are all very melee friendly as a whole, and unlike previous turns, I'd say DRG does worse proportionately to a dummy than a MNK/NIN does because they're all just long, drawn out slug fests - T1-9, the melee difficulty was RNG forced downtime, and I considered the contrary usually true with RNG mechanics that could force GL3 drops. Now it's all about positionals getting compromised with large amounts of guaranteed uptime (other than T10 Wild Charge and T13 Earth Shakers).
Because of the low practicality and application of AoE, I generally look at two things when I go with who I like more on certain turns (ignoring the absolutely balance breaking MNK MNK comp which breaks the rules really bad) - forced breaks and/or mechanics downtime (which hurts MNK far more than DRG) and positional compromise (which right now rapes DRG and is a minor DPS loss for MNK). On a lesser note, BRD DPS (BRD does particularly well T9, for example, and this makes DRG a bit stronger than otherwise). Then you compare training dummy DPS and apply it to these things and you actually get a pretty fair assessment of which melee to bring, in my experience.