This is literally how all the other plot instances always worked. You need to be 88 to unlock the last ones as well.

Technically 12k is cheaper than 15-16K, but I would bet that difference isn't even close to the extra value provided in lucky board. Assuming you are still getting value from the stuff the board drops.

The shop and shop updates are grossly underused by Oasis IMO. It's a brilliant system and while the "star scrolls" feature has some merit, I think the shop currency is really unexciting. If they were updating/including events using these currencies people would care a lot more I'm sure. Instead it's treated like the last stop before garbage town. Tobi was the best ninja in shop now he's useless. They add deidara right before he becomes irrelevant in 2.0, they finally add chikoshudo but no one uses her. People will literally use all the others pains in a ranked team and exclude her.

She's a prime candidate of needed a skill break IMO. Really wish EN Oasis would examine more ways to balance the meta and power levels of ninja. I'm not proposing nerfs, but using systems like skill break to give ninja more versatility. Also I feel like the base stats of some ninja really make them unviable and while ofc power levels vary, with so much BP influence outside of the actual ninja, it really creates a bad environment for ninja like chikoshudo who doesn't have anything special for stats and skills with limited synergistic strategies.

I won't be getting frags of her over medium refines, but if she were in survival I would 5 star her. I already did Deidara without having to buy frags (ninja boxes) and I have well over 80k survival coins with nothing to spend on unless I want to go from 4 to 5 star kakuzu (more useful than either Deidara or Chikoshudo IMO).