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?