Coils of Bahamut... and its inconsistent challenge level.

[aleph_null]

Coils never were meant to be done via DF, if anything they should be put in something like the raid finder to separate practice and clear queues for people who want to do them synced (if any). More importantly the devs don't seem to want to touch the old contents anymore and focus their resources on upcoming new contents. They usually nerf stuffs in the following patch, I don't remember them nerfing contents that were released many patches before. It surely is possible to retune coils for lv 60 players, or nerf it to dungeon level faceroll, but the former would require massive amount of time/effort which will affect upcoming contents, the latter would screw over anyone wanting to do synced clears for challenge. If the devs think those options are worth the cost/risk they'd have done them.

Empty queues are quite normal in this game, have you ever tried queuing for something like gordias or midas savage? Most of them are empty because it's pretty much impossible to clear those via DF (unlike 24 man raids or alex normal), and again the devs don't seem to really care about that. If you want to clear them you'll just have to make a PF.