With HNMs, they are pretty much the Odin/Behemoth fate but I would agree that they should consider a better means of having that content work.
If you take events for example, the Shantoto and DQ quest Fates are actually challenging if you are doing them with less people, they clearly took the time and effort to make mechanics for a challenging experience, but it's for naught when a zerg of 200+ people go in and wreck the creature.
When it comes to HNMs and XIV in general, it should always be about the skill, not who can wait the longest and get first claim. That ugly time sink does nothing more than waste peoples free time and takes the fun out of the game.
When it comes to HNM though, using FATEs would work if done in a instanced manner.
Behemoth spawns, talk to a person and then it puts you into an instance ranked A-Z 32-40 max can enter each instance which would provide with more than a normal alliance but at least still provide a challenge to those in the Fate, <_< not to mentiona chance at gold reward.
However there are other ways to add HNMs to, but they should be done without using time constraints as a main means of obtianing them aka the wait and see method.
Treasure maps are one way to introduce HNM, they alrdy have fights that are basic but at the same time their suppose to be because it's fresh and new, later on more grand and challenging aspects can be added to treasure maps to an HNM like concept.
A treasure map, could start off with a weak group and then unlock another part, as you complete the challenges on the map you unlock further and further to the grand prize. It could be an X marks the spot kind of map.
Say first part puts you intoa location and you have to do x thing before time runs out. Complete it then go to next spot where you have to take down the monster guarding the route to the next area, beat that then the last part you find the treasure and now have to defeat the megaboss protecting it, beat him and you get the treasure.
HNM like concepts like that could be added where the time spent can moreso be on actually playing the game and not just waiting around and hoping something will pop up soon.