I'll just start by saying I got my Animus this week. I spent about 60ish hours on atma grinding and I realize that many have spent longer without success and many have finished in a much shorter time period. I was the second in my free company to start on the atma grind and the 5th to finish due to poor luck. The second half of the quest was less stressful but actually took much longer to complete (4-5 hours grinding myth and another 4 hours per book). Here are my thoughts:

First, this is SE we're talking about. Though this is not FFXI it is made by the same company so there's is going to be some cross over and spiritual succession from FFXI. When relics were introduced into that game the developers specifically stated they were not for everyone. there was an expected timeline of 2 years to obtain one and only a small number of players were expected to see their relics to completion. Many FFXIV players complained upon obtaining their Zenith relics that it was too easy and that they expected something more along the lines of FFXI. And so the atma and animus upgrade stages were introduced. It's not surprising that the quest line brings us back to much lower level content. especially since this patch also saw the official launch of PS4. The intentions of the developers may have been good in those regards but their methods were most surely flawed. Low level players without the use of chocobos could not possibly hope to keep up with hoards of level 50 players. The use of RNG based drops creates large disparities in the amount of time it can take one player to another to finish collecting their atmas. And so their system is flawed. Here's a list of things SE can hopefully learn from in the future and some possible changes they can make to their existing system.

Things done poorly:
High level players gain little from redoing fates on max level jobs.
Low level players cannot keep up with players on mounts.
RNG, it's frustrating, players don't particularly like it. It's odd that on the same patch tokens were added to Coil to alleviated the randomness of drops, more randomness was introduced int eh form of atma farming.

Things done well:
Repopulated old zones.
Introduced more seals into the world to purchase old philosophy items and ventures.

A few simple things SE can do to improve this system is to only have atmas drop from level 20 or higher fates (adjusting zones they drop in as necessary), and to allow some other level 1 item that can be equipped that would allow for atmas to drop. Perhaps an enchanted ring or something along those lines. Another option would be to introduce a system where the drop rate is influenced by fates completed since last atma drop. For example the current drop rate is around 2.5% perhaps they could change this to 2.5% +0.5% per fate completed since last atma drop. This would allow players who have already farmed say 100 fates to have a 52.5% drop rate which would revery to 2.5% once they get an atma. If that sounds like to steep of a buff you could even cap it around 10-15%. Or better yet just have each atma drop from completing a fixed number of fates per zone. Those are my thoughts on how to fix a well intended but somewhat flawed system.

Things for player to keep in mind. This was always intended to be a very time intensive pursuit. It is not for everyone and there are other alternatives. Leviathan EX weapons are i95 and fairly easy to obtain. (The i100 versions are extremely RNG based and not worth the effort) T5 drops i95 weapons as well. If you're not doing or planning on doing coil or EX primals you honestly don't need anything above an i90 weapon anyways. The third option is i100-i110 weapons from solidarity tomes / second coil drops. Do the math, if you're not going to finish your relic by patch 2.3 you're going to be in full solidarity gear (provided you hit cap each week) so you might as well spend your next bit of solidarity on a new weapon.