Just because I’m curious, in what respect is Conan a “partial” package manager? Within the constraints of existing C++ projects and the variance of their build systems, I can’t imagine how to do it differently.

In my experience, most of the value of Conan is with creating packages yourself when needed. You can then self-host a Conan remote and have pre-compiled binaries ready development. Having a conan recipes repository with CI that produces binaries for each required build configuration has become a de-facto standard for projects I have worked on