https://docs.microsoft.com/en-us/dotnet/csharp/language-refe...
Yes, it would. Breaking is breaking.
There are also changes which are breaking in a very non-obvious way, to put it mildly. For example, in C# again, adding any new member to a class can break existing code that happens to pass implicitly typed lambdas to overloaded methods, because overload resolution involves checking whether the lambda body is valid for a given candidate - thus, adding a member can make a lambda ambiguous. I'm not aware of anyone actually treating this as a breaking change for semver purposes, though.
To me it just feels like semantics. They said "here's a new major version of python" when they could also have said "we have forked python 2 and we're calling it python 3. We think it's better and we will probably abandon python 2 at some point".
But it's about setting expectations.
The only problem I ever had with py2 to py3 migration was that it was even possible to have the same codebase run against both, when languages are incompatible to such a degree (most notably, basic type has changed). It basically forced people to make the worst use of the Python dynamic nature (as soon as the stdlib started doing that, there was no going back).
To me, Python represents how not to do language versioning.
