Can you describe how a wordlist and combinator attack is risky for something like eg diceware?

Let's make it easier and assume the diceware list only includes the 26 lower case characters (nothing else), that all words are separated by a single space, that the passphrase contains 7 words. And we assume our attacker knows all of this, and has the same wordlist we used. Heck, we'll even give them our dice too.

How at risk is our 7 word passphrase?