Polymarket is centralized, but one benefit of it is that you can sign up and fund your account anonymously (though you do require an email). Users are not restricted by state or national laws.
On a true decentralized gambling app, email would not be needed, just wallet. It would also be difficult to regulate (the team behind it could be anonymous).
And I'm not saying this is great or anything, but it shows how you can build something with a blockchain that you could not otherwise.
Eth 2.0 will be fully PoS (released fully in the next year or two, but staking is possible now).
Cardano, Cosmos, Polkadot are a few protocols that are PoS but are still very early in their development.
> "we're what, over a decade in to the history of cryptocurrency"
I would argue that's not long at all. The internet was technically invented in the 1960s (ARPANET) and TCP/IP went global in the early 1980s. Took a while for things to get to where we are now.