I don't disagree with anything you said, but I think it's important to point out that your experience is unique in that you're talking about build infrastructure for a massive codebase: most of Google's internal stuff, right?

In my experience plain GNU Make works great until you start working with massive projects. Similarly, the ninja speed improvement: you just don't see it unless you have a truly massive project, or you're using low-quality Makefiles, like what CMake produces. I've measured; I can't see it. I have many medium-sized projects, all with simple Makefiles, and it works really really well. I'm pretty convinced at this point that this should be the way to go for most projects out there.