in the next paragraph I stated the order is not mathematically provable in Dash's design if the masternodes lie
Ok, so you agree that my proposed sequence for creating a fork/double spend is viable?
...And thus Dash is a proof-of-stake security model, not a proof-of-work
I completely agree with that statement; instant-x (and vanillacoin's zerotime) has a very similar security profile to POS chains, and because it has the power to override the POW chain it has been grafted onto, it reduces the entire chain to this lesser model of security.