A soft cap on the amount of runs definitely needs putting in place, honestly don;t really care if it's pretty high, say 20 dungeon runs per zodiac drop.
Point with something like that is there is constantly a light at the end of the tunnel, someone may get lucky and get them in 16 runs or be supremely unlucky but the hard cap means that they're going to take no more than 320 runs.
SE haven't really looked at the psychology behind the current RNG.
The dopamine pleasure response is supposed to be triggered when the drop ( random reward) happens, BUT, for this to really work it needs to rain loot (like in Diablo) or be something where the task can be completed quickly, it's too few and far between in FF14, 20-30 minute dungeons before reward "chance" is too long.

For me personally when it does drop it's not pleasurable, it's relief, and when it doesn't drop I die a little inside cos I just think "here we go this is going to take me 100's of runs". and that is extremely demoralizing psychologically.

oh and as for atma drops, it still took me 5 hours of constant fates to get the southern thanalan drop even after the "nerf"