max reorg depth in NXT is 720 blocks
Checkpoints are centralization.
Mex reorg depth isn't checkpoints.
It is if you expect it to be honored objectively by offline nodes (propagation isn't objective proof because it can be Sybil attacked). I will let monsterer explain that to you, if you don't understand.
May be you will explain us what exactly is centralised in a cryptocurrency (doesn't matter PoS or PoW) whose nodes reject reorgs if they are deeper than the max allowed depth?