It's RNG but it goes in waves. Sometimes you get a string of 80-frag draws, sometimes day on end of nothing or 1-2 Sakura frags. I play 5 different accounts so I see it from different perspectives rather than just 1. The higher you are, the better your "luck" will be. You're just not gonna hit those 80-frag guys at low level very much. The treasure room is also clearly fixed. If you see a Sage Naruto frag, Konan frag, Pains, 30 coupons, Seal Scroll, or the 2X summon scroll you can guess with 80% certainty which card you won't flip. Very rarely you'll get lucky and get everything you want and leave some crap awakening material on the table but only once or twice per week per character generally. Drawing the ninjas in regular survival does seem to be completely random once you account for level. And it's absolutely not worthless to get ninjas you already have 5*. I love getting them. That's more frags to refine for my Iruka and more seal/summon scrolls to get. I have a 4 and 1/2 * Iruka completely for free (nor entirely from survival but at least a 1/3rd due to that.)