Imagine somehow a single party gets 66% of all ETH, enough for them to execute the equivalent of a "51% attack". The community will notice and can decide to do

Imagine somehow a single party gets 66% of all ETH, enough for them to execute the equivalent of a "51% attack". The community will notice and can decide to do a hard fork of the network where they "delete" the attackers coins. So the network would have experience a hickup, but the hacker has lost billions of dollars worth of ETH and can't attack anymore. This is different from Proof of Work & Bitcoin. If an attacker gets 51% of the "mining power" (physical hardware), there's nothing the community can do to "delete" their hardware.