Which part? The inability for 3rd parties to create bootable images instead of using Apple-signed tools? Because that was 4 years ago and is kind of a fundamental requirement for the chain of trust needed for signed system volume security introduced back then.

Or are you arguing that this blog post is wrong in asserting the OS release this week introduced a bug in those tools?

"Resource busy", as opposed to "this tool is no longer supported", almost certainly is a bug, and I don't read the blog post as implying otherwise.

But that doesn't mean it's not reckless of Apple to introduce a load-bearing component that wasn't necessary before and then not properly regression test it across OS updates.