Every OpenBSD release comes with a comprehensive, release-specific upgrade guide which tells you all quirks (including changes to configuration syntax). For this version, you can find the respective doc here:
https://www.openbsd.org/faq/upgrade71.html (Note the entire section called "Configuration and syntax changes")
There's also a pretty clear instruction at the top: "For critical or physically remote machines, test it on an identical, local system first."
I mean, I know it's annoying to hear that, but they are pretty upfront about basically everything with this OS, and you just have to be diligent about actually reading the documentation for the system upgrade. You were not "burned" by the OS or its developers.