The users could reject exchanges and trade entirely on-chain, but that's expensive/complicated/risky.

It is a serious concern for cryptocurrency that most users don't even get the touted benefits because of reliance on exchanges.

> The users could...

Any response that starts with "users could..." or "people could..." is pure wishful thinking and not worth wasting your time on. People don't work this way. En masse they will flow to the path of least resistance, and no amount of wishful thinking will ever change that.

To clarify, I don't see users ever leaving centralised exchanges.

That means classic claims like "bitcoin is scarce" or "transactions don't require anyone's permission" or "transactions can't be censored" or "nobody can seize your bitcoin" are generally false in practice.

Even if a person only trades via bags of cash in dark alleyways and never touches exchanges, they're affected by all this "paper" bitcoin.

If they need to touch an exchange at any point, even if holding in a cold wallet 99% of the time, that exchange can still take 100% of their tokens.

OpenSea is very nearly "entirely on-chain" if I'm understanding your point correctly. It's powered by smart contracts. It's not custodial like Coinbase or Robinhood. Users custody their assets in their own wallets. They trade by submitting transactions directly from their wallet to a smart contract address on-chain which facilitates fulfillment of the trade. The code for these smart contracts is open source and verifiable.

It may not be obvious to more casual observers, but there is a lot of trading volume happening on on-chain exchanges these days (as in easily 10B+ in trading volume per day with most of this coming from futures).

Anyone can generate an NFT, including IP you don't own or existing collections.

Hundreds of wallets might contain a the same monkey picture (or same hash and IPFS link to nitpick).

What matters is that Opensea says you have the "real" one.

Their database is the real list of who owns what, the blockchain is a distraction.

You can see it in their anti-theft systems. NFTs get hidden and blocked from trading after a police report, even if it's still there on the chain.

I would disagree with that characterization. There are dozens of NFT marketplaces which all have access to the same underlying data. An NFT is denoted by its address on chain, which is trivial to find. Similarly anyone can create a website that looks like Google, but the "real" google is the DNS entry at "google.com".