> Vitalik Buterin came up with a solution for the nothing-at-stake problem

Is that a link to an article from a peer reviewed academic journal?

> There are several PoS networks out there such as Cosmos, Tezos, etc, holding more than a billion dollars. If there was an issue, someone would have hacked them by now.

I'll give you a hint: "slashing" is not a thing that sustains security of these networks.

Where did he claim it was a peer reviewed journal?

Don't you think this claim should be supported by some reputable secondary source?