There are a lot of hobbyists, a vast number of people with a Linux box in the corner of the office or a few cloud instances, a smaller number of people running IT for multinationals and one or two people who have whole datacenters to themselves. The larger the system, the lower the computer/human ratio.
I would tend to agree with the OP but with a caveat - most of the people who administer system work on small systems, while most people who's full time job is administration work on large systems. Basically there are an awful lot of people in the world who's job description includes part time system administration.
If I read it correctly there are about 250 million active sites (roughly). It seems unlikely that they are all massive corporate sites.
As an aside, the idea that systemd is a good thing is hilarious to me at the least because it is so brash about making an important change to a huge chunk of the system. Yes the bugs will eventually get ironed out, but in the meantime? Count me out! I have work to do and am not interested in being a free tester for Redhat on my live systems.
The link I included states that those are unique hostnames. Perhaps they are including subdomains on the same ip address, but you might note that rather than quoting the 1 billion sites, I reduced that by their estimated 25% being actually active. Additionally they state that there are on average 3 users per site in 2014. Maybe that doesn't mean anything, but as a rough estimate that all implies far more small sites than large ones.
You don't need evidence for the obvious. There are a few million personal desktop pcs with linux on them, then there are single servers used by exactly one person. Count that against the people working as a professional sysadmin on a big system.
There are a lot of hobbyists, a vast number of people with a Linux box in the corner of the office or a few cloud instances, a smaller number of people running IT for multinationals and one or two people who have whole datacenters to themselves. The larger the system, the lower the computer/human ratio.