Export-Package = -includepackage + -exportcontent. That is, Export-Package will add packages to the bundle, perhaps from jars on the classpath, and also add those packages to the Export-Package manifest header. -exportcontent will only add packages which are already part of the bundle to the Export-Package manifest header.
So -exportcontent is appropriate for Maven and Gradle (non-Bnd workspace) builds where the content of the bundle is being managed by normal Maven or Gradle means.