> zstd does everything in frames and everything in those frames can be decompressed separately (so you can seek and decompress parts). Bzip2 doesn’t do that.

This isn't accurate.

1) Most zstd streams consist of a single frame. The compressor only creates multiple frames if specifically directed to do so.

2) bzip2 blocks, by contrast, are fully independent - by default, the compressor works on 900 kB blocks of input, and each one is stored with no interdependencies between blocks. (However, software support for seeking within the archive is practically nonexistent.)