Solaris realtime OS?

I'm not sure you're being completely genuous with that reponse.
RT certainly doesn't necessarily mean high performance (rarely, in fact, but not impossible in certain circumstances as, iirc, thomas gliexner has previously mentioned that he expected the preempt-rt network stack to provide even more throughput than mainline---I don't think this ever came to pass), or very short interrupt handling, but it does mean that you can offer guarantees of service, which mainline linux can't offer 100% of the time (always ignoring hardware failure).
Unfortunately, solaris has long had the advantage of extensive, and cheap, tracing, and have used this to be able to track down sources of excessively long preempt-disable.
LITMUSrt has a similar facility, but not the resources, or the purview, to do what solaris was able.
Your last line isn't applicable to the topic at hand, though it is certainly true in so far as it must be true.