.7z being there just discredits the entire process. The underlying compression algorithm is a free-hand one and can be anything[0], or contain bugs and exploits[1]. Personally I use only zstd with .7z which is 'non-standard' by the official (Russian) release.

[0]: https://7-zip.org/7z.html

[1]: CVE-2025-0411

I love using zstd, it's so fast to decompress. I especially like that the JavaScript decoder is 8kb and still really fast. Though the 25kb wasm decoders are about twice as fast.

What are the advantages or reasons to use zstd in a 7z container versus just .zst?