Mastercraft Demimateria

If you still think the RNG in this game is influenced by tangentially related stimuli, I recommend also reading up on logical biases and fallacies. You're right that humans make terrible instinctive statisticians because of the basic assumption that two things that happen at the same time are related. An event occurs, an effect is witnessed, and the human brain links the two such that the effect was caused (at least in part) by the event. However, correlation does not imply causation.

The devs have explained their random number generator to us and how they calculate true random numbers, and they've stated that random chances in this game are not influenced by anything other than the random number generator. If they were, their random numbers wouldn't be "true" random numbers. If something has an X% chance, then it has an X% chance. Nothing changes atma drop rates. Nothing changes zodiac quest dungeon drop rates. Nothing changes alexandrite drop rates from FATEs. Nothing changes meld chances to something other than their stated chance. Nothing changes desynth chances to anything other than their stated chance. Material yields from desynth are based on the item and not your actions. Materia yields from converting items is based on the item's level and type and not your actions.

If you want to believe otherwise, you're certainly welcome to do so, but it's simply not true. Your examples still suffer from the "insensitivity to sample size" fallacy. Smaller sample sizes have larger variance than larger samples sizes, not smaller variance. It's far more likely for a small number of i90 SB conversions to yield all tier IV materia or all tier III materia than for a larger sample size. It doesn't mean that the smaller sample size had some kind of outside factor that influenced the yields, it just means that random is random.