Question about PoS

If an attacker simulated an Ethereum network, with 1 million validators in it. He has keys to all validators, because the entire thing is his simulation. He simulates several decades, which in real time is probably several hours.

Then he broadcasts his simulated network to the real Ethereum network, and claim his is the real one. All his 1 million validators start communicate with the real validators. Since his network history has more "total attestations", his network should be the real one according to the chain selection rule.

This is impossible in PoW, because he would need more hash power than all the other miners combined to simulate a "heavier" history. But that is not the case in PoS. I am curious, how does PoS solve this?

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Edit:

I think I figured out the answer. It has to do with slashing, but not the attacker. The attacker's entire simulation follows the protocol, there is nothing to slash, that's the point of this setup.

But any validator who recognize the attacker's chain as the real chain, and start attest on it, they will get slashed (attest 2 blocks with different source). This means no existing validator will recognize the attacker's chain, no matter how many total attestation it has.

The remaining problem is new nodes. A freshly started new node cannot distinguish which one is the real chain. This part requires social consensus. That's the tradeoff of PoS.

Since existing validators will never switch to the attacker's chain. The original chain will always exist, so availability is not an issue. New nodes can always find the original chain to sync once they figured out which one is real through social consensus.