[cc23]

You misunderstand some of the nuances of PoS that make it secure. Along with slashing, there is a period of time during which your staked funds are frozen, where they are unspendable and unsellable. This period is supposed to be long enough such that all nodes sync at least once during that period (think on the order of weeks or months). So if you try to create an alternative history during that period, your funds are slashed (since you couldn't have sold them). And if you try to create an alternative history after that period, everyone will know you're lying, since that portion of the history you are trying to recreate has already been finalized.

Sure, if you get a majority of stake in the network, you can create alternative histories. But, as others have pointed out, this is much more difficult than a 51% attack in PoW.

[nullc]

The text "At most, all slashing does is makes Step 3 take more time." makes it pretty clear that I understand that completely. If you can suggest a revision to my comment that makes it more clear I'd be happy to mae it.

> has already been finalized.

This is presuming the existance of an external consensus mechanism.