QnX is extremely low overhead, and gets a much more responsive system out of the same hardware than a linux based system. Linux simply doesn't do soft-realtime well, forget about hard realtime, even with the patches applied the granularity is terrible, and prioritization is worse.

Those are the things where a microkernel shines. Because realtime systems value responsiveness (and minimal latency) over raw throughput they look worse on paper, but in use they feel a lot more responsive.

In a nutshell, having 300 MB/s throughput for some system function with latency ranging from 2 ms to 100 ms vs having 200 MB/s with latency ranging from 2 ms to 5 ms will give a very strong edge to the slower system if there is some cut-off beyond which the latency becomes unacceptable (for instance, machine or process control).

Lower performance on paper does not always mean worse performance, it depends very much on which criteria are considered to be more important. And latency can be much more important than throughput.