Agreed. In a classroom for sysadmins, maybe make them aware of the distros, but the ones to teach would be a rhel, debian, and aws. Those are the ones used mostly in jobs. I, personally, found Gentoo and then LFS extremely useful in learning how to troubleshoot issues and get a better handle on how to do more advanced things. Doing stuff manually and then forming a good mental model before adding the distro's tooling on top of what does what automatically.
Something I have to do with new sysadmins is having to train them on how boot works, MBR vs EFI boot, what arch they're on and how x86_64-v2 requirement in newer rhels means updating that virtual hardware, how rc scripts and/or systemd work, how to configure a bonded NIC, OSI model and how it maps to how to troubleshoot in linux, etc. To make them more ready for employment, that'd be a help. Also, setting up httpd, tomcat, nginx, haproxy, etc and configure those ciphers! Oh, and automation! Be it puppet, ansible, chef, whatever. At least some experience with a state-based configuration system. I will absolutely argue that the need goes away with proper architecture, but it's a fundamental tool that almost all jobs are going to have.
I know with solaris training back in the day we separated it out to general familiarity and build. Then "advanced" topics like fiddling with driver settings and doing disk stuff (solaris volume manager was interesting).
Then troubleshooting (broken libs, broken boot, broken start scripts) and security. AIX training was different, but AIX is ... different.
If training for k8s, docker, podman, whatever, it's a different story. A lot of that is kind of unique to that environment and will often also be dependent on which of the various bits and bobs are getting plugged in, k8s especially. Containers aren't new, but the OCI standard has made some things better defined.