I honestly did the first couple of lessons using it, as I didn't want to accidentally use a passage that would be explained later on. Plus, you can watch and see where you may have missed something compared to what JY did.
Grammar is especially important for the curve breakers. Here is an example of a curve breaker made all too difficult by grammar. From PT 55 https://7sage.com/lsat_explanations/lsat-55-section-1-question-22/
The test is not graded on a curve, but scores tend to conform to a bell curve. I think this suggests that question difficulty would roughly follow this distribution.