They are hardly even better and much of this I just find is attributed to the simple that that most people have forgotten that newer dungeons can be a bit intense when they are first released.. These days it's just as incredibly streamlined and as incredibly simplified as any other dungeon, IMO.
I just find that it is generally quite wrong to use the argument, when in reality they are both just as disengaging and as uninteresting as they can be, at least with the direction/approach they took to Aglaia and co., - It at least added another method with which to grind with to break up that monotony of just simple dungeon spam or whatever else. We've been doing exclusively dungeon spam > roulettes > dungeon spam in this game for well over half of the games entire lifecycle... Both Bozja and Aglaia broke this trend (and as it stands Occult Crescent is exclusively Lv100 content), Deep Dungeon will allow levelling, but how welcome this is, is very much unknown, and it is a "Too late" situation.
Besides, much of the OP-ness of Aglaia was just linked to the simple fact that the pre-order bonus earrings worked, without this it was only marginally better than standard dungeon spamming, like you were still doing 1 1/2 runs of Aglaia if you wanted to get a level. Can't say I have encountered many issues with queue times of dungeons, like, queue into Aglaia is still a good 15-20 minutes most of the time. A lot of people are just as happy doing FATEs, or using Duty Support/Trusts to level. I've been going through an alt, which doesn't have the earrings, and honestly I have preferred the dungeon farm over Aglaia farm, if the concern is largely around EXP p/h. The queue times dropped off significantly for Aglaia after a couple months, at least on Chaos anyway.
As for the design etc., - It entirely depends really on your mindset. Like, this isn't the first time they've done it. If you wanted to measure purely based on consistent EXP, then doing something like Bozja between 81-90 was just as efficient as doing dungeons between 81-85-ish at which point dungeons took over, and that content was designed for 71-80 in mind, which is exactly the same as Aglaia in this case.
There's definitely a balancing act with older content vs newer content, in the sense that you don't want older content to completely overshadow newer content in terms of raw efficiency (Which I don't think Aglaia falls into that category). But in the same vein you don't want to complete kill older content because it no longer fits within the core content loop.. This is why optional 24-man raids like Void Ark, Ivalice and Nier crossover have just abysmal queue times, because there is no reason to run them.
A better approach would have been to standardize older ones according to Aglaia and then just restructure the earrings so that it works up to 89, rather than inclusive of 90, same with all iterations in future, then you actually put them more in-line with dungeons anyway. - Then you also have the benefit of people more actively trying to queue for older alliance raids outside of just Crystal Tower.
Older content still needs to fit nicely in a content loop, and as it stands with the game at the moment, unless the option content is tied closely to relic progression then it falls far to the wayside which is a problem in and of itself, and something that to a degree the 'unintended' outcome of Aglaia alleviate.
This game treats a matter of choice as a bad thing (in any capacity), and this EXP change made it very clear.