Longest Chain with the Most Difficulty Wins, PoS or PoW
PoS doesn't have a longest chain dufus. That has been the entire point that has been made to you over and over again. There is no work proven with PoS, thus no way to measure the length of the chain relative to any other. There is no computational limit that prevent making a new chain from as far back as the genesis block. The only protection are checkpoints, adhoc social contract, and thus centralization.
How many times does someone have to repeat the same information for you to absorb it in your retarded skull?
FYI2: Proof of Stake Chain Length grows with each Block and its Accumulated Difficulty