While the primary use case for PEP517 build backends is to built wheels for redistribution, distribution packagers are also forced to use them to build their distribution packages. This implies packing a wheel that is unpacked and discarded immediately afterwards. As such, compressing such a wheel makes little sense, as it only wastes time and energy on compressing, only to waste more energy decompressing it a minute later.

In Gentoo, we're usually working around the problem by patching the Python zipfile module to implicitly override the compression level. However, that approach works only for pure Python backends.

Could you please consider accepting a command-line option to the build command that would permit the user to override the zip compression level used? I can attempt implementing it if you're interested — I've been doing pretty well at guesswork in Rust so far.