To be quite frank, needing 12 horns when the FATE only rewards 2 at max is a bit over-kill. None of the other FATE bosses required you to do the FATE more than twice to claim a reward if you gained gold. If they want you to run a FATE 6 times because it's a mount, I'd rather they not make mounts attained through a FATE. While I'm certainly NOT under the illusion of "omgIneedthisNOW," simply camping something that can spawn any time in a window of 36 hours is a hefty price. As others have pointed out, it heavily relies on people working together if you don't camp it yourself. Other times, like what I have experienced, other cliques/linkshells will simply not call it out at all until quite a number of people are already present.
I hope they never put in another FATE reward needing to be run 6 times again.
All of the super bosses are on a 36 to 72 hour spawn window. This includes Odin, Behemoth, Noctilucale (Prey Online), and Ixion. I think Coeurlregina is like Foxy Lady and spawns 12 to 24 hours. Foxy Lady is the oddball out, currently, having no special weather to tell you it's around (even after doing the other required FATEs).