I don't think Apple's developers are any different than any other developers. We all have a very specific definition of deprecation. We even have special keywords we add to our code to indicate something is deprecated. There would be no place to put the keyword if the code was gone

. Deprecation is defined in the dictionary, with respect to software, in this exact way; it's a warning that the functionality will be phased out in the future.
You have a narrow view of "broke". There is a standard practice in software to classify certain intentional changes as "breaking changes". The understanding is that downstream code has to deal with it by changing their own code. OneDrive and Dropbox are downstream from Apple, and this change broke their code.
I really don't know who writes the release notes. Certainly it's not a developer. The word "Deprecations" should have been replaced with the phrase "Breaking Changes".