Belated reply, but not sure if the FFX fight should be nerfed. Don't get me wrong, it's a horribly unfair fight, but I think Floor 8 is where the Dungeon should really start aggressively trying to kill you with the only way to survive being cheese of some kind. dude's team was great, but it was "fair" (and this is a compliment!). Floor 8 has to worry about broken things. For example, any team with Jessica is forced to blow a Magic Burst (but then it's just Yuna / Lulu); Djinn's team with the old Violent Burst Law blows either an Omnislash or, if evading-Limits hype is go, a Great Gospel and still wins; teams with old-Tidus that had Sonic Steel a la Shale's team cast an init. Slowga and clean up; teams with FF5 Bartz can give him Ninja speed where he does something unfair with Mix or Blue Magic to status everything; etc. The fight is of course nigh-unwinnable if too much of the FFX team gets a turn, but that just reflects how tough it is to find a balance for aftergame fights.
Also, something Neph mentioned in #NyarlieDungeon chat: adding RH characters? Switch is interesting in the DL, for all that it can potentially overwhelm the rest of a character's attributes.. Aht notably would be good with just Switch as her only move, as she enables characters like Millenia, Ryu2, or Strago to be suddenly fast on turn 1. Ideas:
Stocke:2.5
Pros: Tanky reviver! Probably survives a Switch, so can make slow characters mildly fast! Turn Cancel is fantastic for later fights if you can stall and build Mana Gague.
Cons: Healing is ST-only and not fantastic. Physical damage fades in the later floors, and his G-Fire is a commonly walled element at endgame.
Marco: 1.5
Pros: Trans-turn. Double turns for someone better than Marco! Healing, revival, and solid Defense / Magic buffs. On later floors, MT Sleep and his buffs go MT as well. Push Assault / Grapple give a positioning game.
Cons: MT healing starts out okay, but is pretty bad by endgame. Below average speed, not that durable.
Aht + Marco: 3.5? (Feels more like 4.0, but using 2 slots may merit a discount?)
Pros: See Marco. For Aht, traps are pretty great damage... once Marco takes his turn. She can switch in slow characters to get the drop on enemies. MT healing, an MT MDef buff, and an MT status resistance buff round out the skillset.
Cons: Aht will probably die if enemies are still alive after she switches. While Aht's MT healing holds up better than Marco's, it too fades by endgame.
Eruca doesn't work (she's terrible on Floors 1-4, and has availability issues for Floor 7, and her claim to above-average speed rests on the Shadowrun dress which makes her super-frail late, and she plain doesn't have early). Rosch is kinda boring, FF1 Knight is already in the Dungeon for PDef tanks and is probably better anyway. Gafka invokes way too much RH grid interp issues. Raynie works but is kinda bland and not that great for the Dungeon.