I’m scouring through the comment chain but I’m not really finding such a definitive response. I’m assuming you’re referring to the first chain of comments, but that seems to boil down to “the attack exists but it’s fine because to successfully attack the network would destroy the network, and with it any profit you’ve made in the attack; thus you cannot profit” — but this is directly addressed by the “nothing at stake” section of the article; if I can attack the successfully attack the network, and liquidate my position before the network implodes, I win (which PoW mitigates by making the 51% attack itself prohibitively expensive). Which hardly seems unreasonable, because the network imploding is a feature of humans losing trust in the network and abandoning it — in compute-land, an eternity.
In my skimming, I can’t find anything that addresses this — and especially not anything that merits describing TFA as a strawman.
The writer of the article supposes that it's a critical vulnerability that a validator can come up with an "equally valid" alternate history for Ethereum that stems from a fork several months prior, after the validator has already withdrawn their stake from the canonical chain to prevent slashing.
In reality, everyone just ignores the attacker's chain, because it attempts to rewrite not seconds, minutes, or days of canonical history (periods of time short enough that the identity of the canonical chain might be in question), but many months of history that the entire world has already agreed on and that node software refuses to reorganize the chain past.
This post by Vitalik in 2014, shortly before the launch of Ethereum, explains why this "weak subjectivity" property of PoS is not nearly as problematic as PoW proponents make it out to be.
To execute that attack, you would need validators to sign blocks on your forked chain. Presumably they’ve already signed blocks on the main chain, so they’d be double-signing, which instantly costs them a very large amount of money on both chains (when you double sign, people can submit proofs of that on either chain, causing you to get your stake slashed.) That’s what makes the attack you’re imagining prohibitively expensive.
If you’re still worried about that happening to some ETH you received, wait for the blocks to finalize. Once they have, they will never be reverted without a change to the protocol.
