tl;dr, dungeons are basically not even worth running in this current patch because dungeon drop rates are abysmal across the board.
Rebalancing of drops is needed, whether its through tweaks in the elleon marks shop/drop rate, or just increases in drop rate in dungeons in general. The current model is really destroying players' motivation to run dungeons at all. Personally, my favourite solution would be a guaranteed reward through vanguard quests (added to the base vanguard quest), as was used in the past with dark shard armor feed. Maybe something like this:
Gossamer Vault: 1x improved weapon feed and 1x improved armor feed per run via vanguard quest
Ruinous Manor (Normal): 3x Improved armor feed per run via vanguard quest
Akalath Quarantine: 2x improved weapon feed per run via vanguard quest
Catalepticon (Normal): 1 Lumikan's Wing Fragment per run via vanguard quest
Catalepticon (Hard): 1 Lumikan's Horn Piece per run via vanguard quest
These additional items must be effected by increased vanguard item events, thereby adding much needed value to these events. Perhaps accessory and infusion stone boxes could be added to their respective dungeons as well.
Ultimately, there needs to be some consistency with drops from dungeons, so that players can see that their spent adventure coins and time will consistently reap them some kind of reward. Items delivered through vg quest can deliver just that, with daily caps already in place to provide a reasonable limit-gate to progression.