Explanation

The critics misjudged the designs, so you know that the word in the blank must mean the opposite of epitome of high fashion. Choices (B) and (F) give roughly synonymous meanings, but nothing in the sentence supports the idea that the designs were expensive.

Neither defamatory, which means libelous, nor contrite, which means remorseful, is supported by the sentence, so eliminate choices (A) and (C). Both mundane and insipid can mean uninspired or ordinary, so choices (D) and (E) give you appropriate, equivalent sentences.
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why is mundane meant to be tasteless or boring? thought it was meant to be very generous?

Mundane basically means something simple and for the workday. Quotidian.

In the case of fashion clothes, they are not luxury but normal. And this was the critique moved to Chanel.

D and E are the only synonyms among the answer choices.

However, it is not a good question.

Regards
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yaa for sentence equivalence, i prefer to first make the synonym pairs before even reading the sentence, automatically lots of choices gets eliminated. then read the sentence and decide which pair matches the blank.

great explanation

Agree this does not seem to be a good question.