I think story mode is easy enough as-is. My SO has cleared every storyline-related dungeon and non-EX Primal battle, and this is about the only real video game she's ever played for any length of time. She had some stress early on, sure, and she still gets nervous about new fights, but within a run or two she's mastered everything and is venting to me when others mess up mechanics. Certain fights take longer - Hashmal in Rabanastre gave us both a bit of trouble for awhile - but I've never heard her complain about the game's difficulty, despite being in all respects a neophyte, introverted, anxiety-prone gamer.

The only change I'd like to see to story missions at the moment - and dungeons in general - is an absolute, iron-clad guarantee that there will either be a solo option, or there will not be any component of the dungeon that conflicts meaningfully with the speed-run meta that has existed ever since ARR was released. I'm still frustrated, for instance, that I can't enjoy the random little notes and such in Fractal Continuum (Hard) without setting up a pre-formed party. Obviously this applies even more to the atrocious handling of the two MSQ 8-person dungeons at the end of ARR.

The difficulty, though, is already easy enough, IMO.