From my understanding, and perhaps I'm mistaken... Coil is "supposed" to be story-related content. While it's not "Main Scenario," I think SE intended for everyone to be able to clear the content at some point.

As it stands, Turns 1-4 present little difficulty for people who are over-geared, while Turn 5 is a mechanics check. You can mitigate the difficulty of Turn 5 considerably with gear (Conflags are easily DPS'd, Dreadknights die fast, Death Sentence is like a baby's kick, etc.), but you still gotta deal with more strenuous positioning mechanics which can cause a wipe.

The Extreme Primals however... I don't feel these should even have an Echo applied. These are supposed to be optional fights. Challenge modes. The rewards for beating the Extreme Primals fall into the "nice, but optional" category.