It's been mentioned already, but it'd be a huge help if they cut out all the nonsense boring fetch quests from old content. Pull them out as option side quests, whatever, just don't make me run halfway around the universe to buy someone his favorite brand of cup noodles or whatever.

That's not limited to ARR either... parts of the Rabanastre unlock quest were so completely uninteresting and unnecessary (lookin at you, weird minstrel guy or whoever you are). Stuff like that, that doesn't advance the actual main story in any way whatsoever, could (relatively) easily be cut out or made optional, and that would make the story easier to follow and (imo) way more interesting AND quicker.

And maybe just... lock less things behind the story. Let people unlock dungeons at least by going to them in the world, or just when they hit the right level, idk. Though I had a friend who had the opposite problem and didn't like having to do dungeons every few levels because he wanted to just do the story and progress, so I dunno how to reconcile that. There's no way to really make everyone happy, but there are definitely some improvements they could make without just letting everyone skip everything.