I'm not that concerned about build time performance. I'm more concerned about how easy it is to fit into our Yocto based build system. I know how to integrate autotools projects, plain makefiles, and even cmake. I'm not sure what's involved in integrating Meson.
I'd consider this a plus, given that plain Makefiles are usually tragically less performant. Plus, Meson doesn't *only* target Ninja: it generates Visual Studio project files, and the Meson maintainer is working on improving the XCode support.