As the opener of this post I did solve my problem by leaving Enpass. I am now using the iCloud keychane which is (yes) missing quite a few features but is very convenient to use and very well implemented in the Apple ecosystem. It might not be the right solution for everyone but it is for me. I also am now using the mask mail feature from iCloud for every service. It took my quite some time to change this but now have a bit peace of mind. I absolutely agree to what Discordant wrote. Adding aliases doesn't help to protect your privacy if you look into the advanced headers of a mail.
Convenience always wins so I believe it is not the question if such a feature should be implemented into Enpass but when. Maybe I am going to return to Enpass later again.
1Password is not an option for me since they chose Electron to develop their new App for macOS.