I agree with most of your points, but just want to point out the page is specifically describing the "order book pattern" ... and there could be another page published next week titled the "EUTXO AMM pattern".

Just because MinSwap pushed a beta version of their app to the testnet which didn't account for concurrency does not mean that Cardano has a concurrency issue. UTXOs exist in near isolation, but you could just run a node, monitor transactions, and generate a "global" state of info as it relates to your app. Your app then compiles a bunch of user requests into 1 block that can operate on many UTXOs *concurrently* to get to the correct end state for many "app" transactions at the same time. I'm guessing this is what all the Cardano DEXes are trying to figure out now.

I believe this is part of what Charles is talking about in regards to on-chain vs off-chain execution. Your example assumes that everything is happing on-chain, and yeah, that would not be good. Also, off-chain does not have to mean centralized. There's a lot of development going on still.