How about the following scenario:

Package A is SemVer 1.2.3, package B is PragVer 1.2.3. both A and B have big release with breaking changes and marketing hype, so now they're both at 2.0.0. It is later found that in version 1 of both packages there is a bug requiring a breaking change in order to fix. B (pragmatic) can apply the fix to version 1 branch and release it as 1.3.0. How does A (semantic) make a breaking change on version 1 and version it correctly?

TL;DR Pragmatic Versioning enables breaking changes on LTS versions.