An American lawyer has analysed 600 appellant briefs written for three courts in the USA. He found that the simplest writing style appeared in briefs written for the US Supreme Court, even though the court decides complex questions. Average sentence length and use of active voice were good in all three courts, but best in briefs written for the Supreme Court. Briefs for all three courts were full of hard words and wordy expressions, but less in briefs written for the Supreme Court than for the other two.
Writing that Wins: An Empirical Study of Appellate Briefs, 31 July 2017. (The analysis is flawed by wrong assumptions about the StyleWriter software used to measure writing style; my summary is based on the figures published in Table 1.)