It's completely circular. It's like the Bible trying to proof itself. With no anchor to the physical world, you can't actually ever know
I'm not saying that requiring clients to log in every 4 months is a reasonable security assumption, just showing that hand-waving it as "completely circular" is incorrect. It's more nuanced than that.
Good luck with that https://en.wikipedia.org/wiki/Too_big_to_fail
With Ethereum PoS. It is dependent on ETH being distributed to many individuals. If only a few individuals own most of the ETH, then they will then have the power dictate what is the "truth" in the blockchain. Right now, ETH is very well distributed around the whole planet.
As you can see, one is oligarchic, the other is very democratic.
Ethereum is not a Corporation that is designed to make profits. It is non-profit, it's not even a company, it's simply a protocol implemented in Free Software.