Enforcement of Guideline 4.3 is important to Apple because, as Apple informed your client, duplicative apps “create clutter, diminish the overall experience for the end user, and reduce the ability of developers to market their applications.”
BlueMail and TypeApp are neither spam nor duplicates, but Blix voluntarily removed TypeApp in May 2019.
As Blix notes in its amended complaint, there are numerous apps in the App Store that would technically fall under the same “duplicative” definition. Apple has not sought to eliminate them in any way, which shows how selectively Apple enforces its App Store Review Guidelines.