It doesn't follow any existing patterns, which makes it harder to learn if you're already familiar with troubleshooting init prior to systemd (troubleshooting which would have started with a quick trip to /var/log/dmesg and stopped with /var/log/syslog).
So yes, it can absolutely be learned. But existing administrators have to abandon most of their existing toolkit to do so.
That all said, that's not what I mean by opaque. By opaque, I'm referring to how many (few?) people truly grok what's going on inside of systemd. As an arbitrary point of measure - systemd (and only systemd) consists of over 500,000 lines of C code. It takes a lot of dedication and time to understand what is going on in that much C code. There are, by GitHub stats, less than 10 people who have contributed (combined additions and deletions in commits) to even 1% of the codebase, and only 4 who have touched more than 50%.
In comparison, sysvinit consists of about 9,300 lines, and upstart 115,000.