Chase mission can sometimes give that white cat 5 frags so he is still available.

I do agree that unpopular ninja are harder to get due to them not being requested (They could be added to the survival ninja frag pool as rare to be honest)

Newer players can't expect to get like 20% of the ninja due to them unavailable 95% of the time in any way.Even when available going for them is just a waste of coupons since they're not that good .

Worse is that some of them are in ninja collection which means stats impossible to gain ...

Problem with survival is,that,even if those ninjas are added,their drop rate is too low.Like DPB Hidan for example.By the time I get all 3 young sannins,suit Sai,Hebihime,Zaku,Udon,Moegi,Konohamaru at 3-4 stars,it drops only 10 frags of Hidan.His drop rate is lower than edo jinjurikis or 8 tail Bee.Only ninjas frags more rare there is Sasuke susanoo.