As with all Gacha games you can talk about luck and distribution but unless it has an inbuilt system that Im not aware of like Fire Element Heroes (your % chance to roll a 5 star goes up for every time you roll and dont get one) or Hearthstone (you are guaranteed a legendary after 40 packs) its just simply luck of the draw, and it doesnt strike me as any more unfair as most gacha games. I can share my own personal experience of:

Rahab event, rolled a 3000 jewel gacha and bought a 10 ticket too, got a single SR kami and that was it. Noticed I had 2 random gacha tickets from dailies sitting there - used them and rolled SSR Amaterasu followed by SSR Dark Kaiser Dragon on 2 individual roles. ::WTFFace::