My understanding is that chaining compressors is a classic technique for image compression. IIRC PNG and Basis are both implemented as initial transformation/pre-filtering/conditioning pass(es) designed to make the image data more compressible before feeding it to a codec like gzip or zstd.

This definitely works for things that aren't images too. I previously proved that you could improve the compression ratio for WebAssembly significantly by performing lossless transforms on the module before feeding it to gzip or brotli (though the gains are much smaller for brotli since it's so good to begin with): https://github.com/WebAssembly/design/issues/1180