An extremely detailed retrospective of how systemd came to be, how it evolved, and what it actually is (an init system? Ha!): https://blog.darknedgy.net/technology/2020/05/02/0/

It's a long, long, long write-up, but it's probably the most worthwhile piece on the topic. The author took the time to re-read some old emails and demonstrate how the declared goals repeatedly changed over time. Also an interesting break-down of systemd's technical deficiencies, and how they didn't stop the adoption.

If you were looking for a definitive analysis of what happened to Linux in 2011–2015, this is it.