'tuned' for the brotli dictionary is a bit generous [1], but yes, it contains a smattering of strings [2] you'd find in plain text and web documents.

Because of its seemingly haphazard dictionary, I wouldn't rule out zstd outperforming brotli, if trained on a good dataset.

[1] https://news.ycombinator.com/item?id=12010313

[2] https://gist.github.com/klauspost/2900d5ba6f9b65d69c8e