I mean, the study itself seems to disagree with that sentiment:

A principal concern for us was to test whether the subjects had reached a level of “proficient-prose literacy,” which is defined by the U. S. Department of Education as the capability of “reading lengthy, complex, abstract prose texts as well as synthesizing information and making complex inferences” (National Center 3). According to ACT, Inc., this level of literacy translates to a 33–36 score on the Reading Comprehension section of the ACT (Reading). Literary prose can be even more difficult to comprehend because it requires the ability to interpret unfamiliar diction [End Page 2] and figures of speech. Dickens’ novel worked we [sic] as an example of literary prose because his writing contains frequent complex sentences and language that often moves from the literal to the figurative. In Bleak House, Dickens also mixes specific, contemporary references (from the book’s first publication in 1852–3) to his 1820s setting.