One of the main reasons for dependencies required to be in build.zig.zon is so that there is a canonical, simple, declarative place to list all the dependencies of a project. This is useful for all kinds of tooling, including third party stuff like package indexes which want to know which packages are depended on the most.
The use case you are describing goes against that premise, so that’s why it’s an uphill battle. Personally I don’t find those bulleted points against having the declarative file compelling.