just some insight on this

The final reward is not shown on the event page, the achievement for it is hidden in game until unlocked, and the event you get for doing it pretty heavily suggests you did something special and unexpected.
Strongly hints at them not expecting a majority to complete it, can even quote game devs on this fact

The length of the event is pretty extreme letting people take their time and it will become easier as time passes for the dedicated(believe it or not fates go a lot faster with less people, if you have a zone to yourself they're a breeze and I've already been able to get zones to myself a few times)
Just do a little at a time, you'll get there without burning out if your diligent

It's good to have events that appeal to various gamer types. I know a lot of people that are happy to have an event that's not exhausted within an hour for example
the first rewards are instant for the instant gratification crowd
the minions are guaranteed and quick, the first few weapons are easy, and the first mount is reliably obtained for the more casual
the latter weapons and second mount are a hell of a grind for the hardcore, grindy, willing to do a ton for some small special reward group
(if you actually have all 13 jobs leveled to use the weapons you've already did a lot more grinding than this even will possibly take for even the most unlucky)

despite what most seem to think the "glowy whisper mount" is not the only reward. There's a glamour bracelet, 13 minions, 13 glamour weapons, and 2 mounts. Pretty sure that's probably triple or more what most events have to offer and most of it is easily obtained while also leveling jobs and the event is also overlapped with moonfire faire and anniversary there's a lot going on all at once event-wise

The event is also lined up with free play time, if everyone could finish it in a day it wouldn't do much to populate the old world zones for possible new players to see activity

and finally, not all content will appeal to all players. It's just a plain and simple fact
I don't really care much for deep dungeon though i know people that have grinded out 4-5 weapons out of that already which i think is way more of a tedious RNG grind than yo-kai
I absolutely love aquapolis while my gf thinks a bunch of guys cheering for a door opening is the stupidest thing she's ever seen
to each there own

if you just want one or two minions and a weapon, if you want to iron man grind out a mount that is not very discernible from an easy to get one, if you want to take it easy and get everything over months, if you just want to outfit your favorite jobs with glamour, if your just an avid minion collector; this event does have something for most anyone