In my opinion, the latest batch of dungeons were just about the ideal difficulty. In terms of sheer mob damage output they are kinda week compared to the average group, but in terms of actual fight mechanics they can surprise you. Just looking at the final boss of each dungeon, Giruveganus has a whole bevy of unmarked AoEs requiring you to memorize its 'tells', and then be able to split your attention between two bosses who can't be tanked; Avere Bravearm, while himself a simple 'tank-and-spank' boss, is supported by AoEs all over the place and a massive AoE that you can't tank through unless you actually pay attention to said massive AoE's gimmick; and even now, I still wind up with the occasional random ally in Hullbreaker who doesn't realize that the green symbol over them means they need to move to a different island or else there's a very good chance we'll wipe. And, of course, everyone has their own horror stories of horrible ST runs.

As FFXIV goes forward, I imagine SE will come up with increasingly interesting fight mechanics that are a combination of "Pay attention to this gimmick or you all die" and "You can tank through this but it'll hurt" fight mechanics, allowing for difficult dungeons without ever having to actually buff the minimum required iLvl past what can be easily attained by 'casual' players.

Just my two cents on this subject.