I don't quite agree. I think they're about reducing the size of your kernel, and moving the complexity of operating system service details into separate process

I don't quite agree. I think they're about reducing the size of your kernel, and moving the complexity of operating system service details into separate processes, where they can crash, restart, be upgraded, etc. in isolation, in their own terms. The analogy is like microservices vs monolith, but with kernels, not big applications.