first I'd like to indicate what you need to successfully accomplish the PoS attack you pointed to.
a) disable checkpoints and have users download your release.
This is obvious. Checkpoints completely centralise control of the chain, though.
b) procure many PoS accounts keys with very large stakes.
Historical keys have no value, they should be easy to purchase.
c) have powerful / quantum hardware to build a myriad of chains to get one with the cumulative difficulty higher than the valid chain to be accepted by other nodes.
Since block production is so cheap in PoS, I don't need any such powerful hardware to do this.
Now for the theoretical attack vectors on PoW, these are well known but I can't refuse since you asked.
1) voluntary collusion of miners.
Yes, 51% attack is well known.
2) involuntary - high vulnerability of centralized mining physical infrastructure and known locations to state level attacks.
The chain is highly resilient to such takedowns - anyone with a CPU can mine. In PoS, if you confiscate the stake from the stakers, the chain is totally unrecoverable.
3) dependence on ever increasing hash rate and difficulty, security is weakened if price goes down, dependence on energy infrastructure.
Security is weakened if
hash rate goes down, not price.
4) quantum computing.
Does not exist.