With Coil, it wants you to clear the first one before 2nd coil because it's a story thing, one follows the other. For extreme mode primals I don't see why they should need to be done in any order... beating Ramuh (story) should be the only requirement to unlocking Ramuh (extreme) I think. As for competent players abandoning old content, hopefully things like echo and adjustments make it possible to beat them with a DF party... at the moment that is not the case, but maybe eventually.