I freely admit I am out of my depth and have nothing educational to add on the subject. I have but four things to add on this subject:

1. Oh! It's "d.i.l.l.o."! I misread that as something else.

2. After reading many comments in this thread, I must admit I am stupefied at the sheer amount of stuff that can go into merely setting up and maintaining a version control system for a project.

3. I have cited every one of the same problems OP enumerates as my argument for switching new projects over to self-hosted fossil. It also helps a good bit with #2 above when you're a small organization and you're the sole software engineer, sysadmin, and tier >1 support. It's a much simpler VCS that's closer to using perforce in my experience. YMMV, but it's the kind of VCS that doesn't qualify as a skill on a resume.

4. I also find GH deploy keys frustrating because I can't use the same key for multiple repositories. I have 3 separate applications that each run on 4 machines in my cluster, and I have to configure 12 separate deploy keys on GitHub and in my ~/.ssh/config file.