Sentence Correction (SC) | Re: The central issue before the court was how far the regulatory agencies

I am so confused with the parameter on which a question difficulty level is judged.
If I go by Gmatclub rating this is a 700 level question 75% difficulty and <50% correct answer.
I also got this question incorrect.

This question is originally from GMAT Prep QP2 and categorised as a Medium difficulty level question.
Which I believe is incorrect categorization.

There are many such instance where a question appears really easy but in MBA.com categorised a Hard.

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