If that's about using predefined dictionaries, zstd can use them too.
If brotli has a different advantage on small source files, you have my curiosity.
If you're talking about max compression, zstd likely loses out there, the answer seems to vary based on the tests I look at, but it seems to be better across a very wide range.
No, it's literally just compressing small files without training zstd dict or plugging external dictionaries (not counting the built-in one that brotli has). Especially for English text, brotli at the same speed as zstd gives better results for small data (in kilobyte to a few of megabyte range).
If brotli has a different advantage on small source files, you have my curiosity.
If you're talking about max compression, zstd likely loses out there, the answer seems to vary based on the tests I look at, but it seems to be better across a very wide range.