Look, all I am saying is properly designed PoW and PoS have their advantages and flaws. Dismissing one or the other is ill-advised. Hedging your risks using both is wise.
I haven't seen an instance of a PoS chain which didn't rely on rolling checkpoints to prevent against long and short range attacks. If you don't have rolling checkpoints, anyone with historical private keys can re-write history.
Why would an empty private key have any value to anybody?
Rolling checkpoints do not centralize control of the chain, they are a feature of decentralized consensus, what makes them evil in your eyes?
An empty private key may have no value to someone. The problem is you need to obtain a lot of them, the longer you wait the more spread and larger is the hashing stake protecting the network, making your task more arduous, and this is only one challenge you face. I illustrated the other challenges in the preceding posts.