It's not FUD. Measure system call latency on Fuchsia and Linux for a simple read(), and you'll see Fuchsia is slower. It's the context switch that kills you, not the copies. Of course you could use FUSE on Linux and it would be just as slow.
Now go do same with INTEGRITY, QNX, L4 and plenty of others used in production on real time scenarios where Linux is found lacking.
UNIX clones, Linux and BSD variants are the surviving monolithic kernels.
On embedded space, most high integrity OSes are microkernel based, Apple and Microsoft OSes are hybrid variants, and as shown at this year's WWDC in a couple of years Apple OSes will only allow for user space drivers.
Even Android now uses a mixed model with userspace drivers (Treble compliant ones) and the standard Linux drivers (Treble legacy mode drivers).