Since nobody else seems to have picked up on this claim, I am going to ask what you mean, because the only simplification of dungeons I am aware of was because they couldn't get Duty Support NPCs to handle dungeons with unique and interesting mechanics. The other side of old dungeons feeling too easy now is all the potency increases retroactively given to job abilities as the jobs developed (due to SE's, "we never want to take away, so every rebalancing only means making some job's numbers bigger" approach), moving player power further and further away from what it was when those older dungeons were made.
But I may be wrong -- in what instance were older dungeons revamped as a dev response to players complaining about them being too difficult?