I'd really like to see this broken down by established vocabulary and made up vocabulary. I think that would really start to show who were the best lyricists on both ends. Rappers with a lot of made up words might be on the far left, and rappers with a lot of unique words that aren't made up would be on the far right. Both sides of the scale would show rapping talent on different dimensions. Influential rappers like E-40 who add new words to the vocabulary, and wordy rappers like Aes on the right who use a really dense and descriptive vocabulary.