Earlier quoted context omitted.
A quick Google search suggests English has about 10 bits of entropy per word. Having a long password like that can still have high total entropy I suppose, but it has a low entropy density .
Maybe 10 bits is the average over the dictionary – which is what matters here, but over normal text it is significantly less. Our best current estimation for relatively high-level text (texts published by the EU) is 6 bits per word[1]. However, as our methods of predicting text improve, this number is revised down. LLMs ought to have made a serious dent in it, but I haven't looked up any newer results. Anyway, all of…
The diceware method is supposed to generate totally random words, so it should fundamentally be unpredictable unless there's a flaw in the source of randomness.