There is no progression, only 'will I be lucky enough this time?'
There is nothing to work towards. In every other event, you can set a goal for yourself and play until you complete it. This event has none of that. There is only one goal worth having, the book, and it is so rare that it doesn't matter how much you farm, you still probably won't get it.
It's ok to have an impossibly rare drop in an event, but it can't be the point of the whole event. The event boss is locked behind a ultra-massive RNG wall and that's just sad.
I agree that the luck and reward are both set too high in this event. But there is an intermediate goal, toward which to work: Get 70 Ancient Pages, so that you can get the 3-star Black Kat helmet. Its offense is just as good as any Black Kat armor. Its defense is not good, but one doesn't wear this armor for defense. So it's a nice lower-level reward.