there is no way to predict which SN will get the next transaction as it is based on human behavior
Ahem. You need to prove mathematically and holistically that is a random process and not subject to game theory. That is essentially the fundamental problem with PoS, its entropy is bounded unlike PoW where the entropy is external.
relate to the assertion that bounded entropy is bad? Bitcoin's reused R value attacks arise since it requires new entropy for each transaction, while with the curve25519 this does not seem to be the case.