because theres no exp dungeon, and you need to pass story's minimum battle power if you want to breeze it
so, how to level up and gain battle power quickly? by using exp book, and that dropped from normal stages.
also all characters available so far are SSR.. or not.
if all characters are ssr then its the same as no SSR to begin with.
and the pool got diluted with weapons, so character from summon are extremely scarce. use story unit if you are lucklet