[rwmj]

> I thought newer microkernels... Reduced that? Fixed it?

They have.

Actually the elephant in the room is modern hardware which makes even syscalls into monolithic kernels expensive. That's why io_uring and virtio perform well - they queue requests and replies between the OS and applications (or the hypervisor and the guest for virtio) avoiding transitions between address spaces. Any operating system in the future is going to need some kind of queuing syscall mechanism to perform well, and once you've got it doesn't much matter if you structure the components of your OS as a monolith or microkernel or something else.