I have already explained upthread that
Proof-of-Stake is not secure because essentially you must trust those with the largest stake (and it can't distribute new coin out to the people through mining in a competitive manner).
It seems to me that the creator of Nxt fixed PoS by adding
Transparent Mining. He also invented another "mining" algo that doesn't use "coin-days".
You see they tried to solve it by invoking trust and reputation "knowing who all the miners are", but I already explained upthread that is just another low entropy (i.e. low security) result:
I strongly posit proof-of-stake will be proven insecure. It lacks the expanding entropy of proof-of-work.
Trust via reputation (i.e. social capital) or stake (i.e. capital share) inherently
degrades to centralization and low entropy outcomes.