Some of the hardest contents in this game aren't really meant for DF (look at alex savage for example), coil was such content for lv 50. The devs put everything other than the latest raid tier into DF, after nerfing some of the mechanics, but some floors don't outright become faceroll after the nerf. Some of the floors are outright impossible to clear without hours of practice (see a8s), which is why I hope they'd put all raid contents in RF since there are separate queues for practice and clear, but that's a separate discussion. They're incredibly difficult to run at lv 50 because they were meant to be the most challenging contents at the time. Coils and alex savage are completely different type of contents from dungeons, normal mode raids and 24 man raids. They are/were meant to be difficult.

Generally the devs don't seem to want to put much effort into outdated contents. As I've mentioned in a previous post some lv 50 ex trials would trigger instant wipe mechanics due to excessive dps, and sometimes you really need to stop attacking and stand still for a while just to avoid that, which clearly is a bad design for a game that allows overgearing. You just need to find a way to work around the mechanics.