I can't tell for the difficulty part, since i'm actually fine with the current syste. For my wife a mid difficulty could help her since she lack of selfconfident for extrem, it might help her passing the gap and go in extrem fight.
For the bahamut coil i think a "normal" version should be had so people could enjoy both the fight and the story and the current version could be renamed as "savage" just as the other 8 man raid