SELinux is great for areas that are into DAC/MAC/RBAC, plus the aforementioned lengthy support. I see more and more customers wanting Red Hat/CentOS than any other Linux distro and for good reason. It just works. Things like CPanel only run on these distros. Red Hat/CentOS are also very predictable and they offer superb documentation. More and more people are uncomfortable with things like Debian because there is no throat to choke if they need support or if something goes pear shaped.
I have worked on Linux for 20 years now and I have never, ever seen Debian or Slackware or even Ubuntu in a TRULY mission-critical role. People may disagree, but there are reasons why Red Hat/CentOS are chosen. They are typically very stable, use tested software, and are well documented for the use cases they excel in. Red Hat runs some truly mission critical stuff like power grids, and more and more SCADA systems, now that they are being upgraded due to threats.
How about a router? I've been considering getting some single-board computer (probably an APU2[1]) and turning it into a router, possibly using OpenBSD + pf. Or maybe just install Pfsense. Or maybe use Linux and...iptables? (Not sure how that stack would look exactly)
OpenBSD shines because of the ongoing code audit, the minimalism, and the ability to easily make it into whatever you want. I don't care for any other OS for serious business. I will almost always use OpenBSD for servers, with RedHat or CentOS being the only other choice because of SELinux.
I would also venture to say that OpenBSD has the absolute best documentation of any OS out there, even better than FreeBSD.