It's a well established proposition (at least on the English forums) that end game content is horrible broken at least with regards to melee DD. It is also well established (again by the English playerbase) that the issue is endgame reliance on AoE attacks that cannot be blocked and are capable of instantly killing all non-tank DDS with one or AoE enfeebles that apply crippling affects that cause death or are unremovable. I think it would be possible (though admittedly time consuming) to take the current content and make it more melee friendly. Here are some suggestions.
1. Buff HP across the board. Won't fix everything but it's cheap and easy to implement (and probably well overdue.)
2. Limit a monsters TP selection. The problem most content is that mobs select tp attacks at random. That means it is impossible for a party to know whether the monsters next attack will be the AoE attack of insta-death or something that is manageable. Again there are options for how to handle tp attack selection:
a. Make most AoE, high damage attacks dependent on a condition precedent (like how Wyrms only use spike flail when hate is drawn by a player attacking from behind). If attacks can be avoided through game play, it at least makes bad game play the reason for a party wipe and not bad game design.
b. Routines. Ok, so I hated the FFXIV battle system because of this, but in FFXI terms it could be useful. If players have advanced warning that an AoE is about to occur, because the monster followed a specific pattern of TP attacks, then melee players could be out of range when the attacks are used.
c. Increased prep time for TP attacks. If players have long enough to respond from the time the monster initiates a tp attack to the the time it is used, then the players have a chance to run out of range.
d. Increase the instances of proc and lock. Give players the chance to disable certain attacks from being used by procing a weakness. Weakness procs should not last the entire fight, but the system should provide some notice when the proc wears off. That way a party that is paying attention can lock out the most deadly abilities.
3. Make the most debilitating debuffs single target.
4. Or make AoE debuffs avoidable via one of the methods mentioned above (see 2a-d).
5. Remove debuff auras that cause amnesia, death, silence, etc., unless the aura is of a very short duration and that debuff wears off by moving out of range.
6. Increase the potency of Stoneskin and other methods of damage absorbtion so that the amounts absorbed are actually life saving.
7. Add more means of debuffing, enfeebling monsters that directly correlate with the survivability of TP moves.
a. Amnesia!
b. A spell that increases the readying time for TP moves in a method similar to Addle's effect on spell casting.
c. More, stackable, methods for signficantly decreasing attack power and accuracy of monsters.
These are just a few suggestions and I'd welcome more. Please try to avoid suggestions which decrease the abilities of other jobs though. The purpose is to make every job playable not your job playable at another jobs expense.