Every string seems to start with "very", "much" or "such", and the page does explain this reduces the entropy. I wonder if it could aid a known plaintext attack[0]?

[0] https://en.wikipedia.org/wiki/Known-plaintext_attack

It can't, as per the BIP39 spec[0], the mnemonic is run through PBKDF2 to generate the seed that is actually used.

So even knowing one or two of the input words doesn't tell you anything about the actual seed.

[0] https://github.com/bitcoin/bips/blob/master/bip-0039.mediawi...