For very similar reasons out of frustration to not being able to fix basic contacts syncing issues and improve those apps, we have been building a contacts app for Cloudron from scratch with some decent UI but more importantly a carddav server which we can fix for all use-cases we can test. It is still pretty fresh project, but works well at least with thunderbird, davx/davdroid, gnome.
@foliovision if you like, give it a go and if you hit syncing issues just open a thread at https://forum.cloudron.io/category/221/contacts any other feedback or bugreports are of course very welcome to get this going.
The project lives at https://git.cloudron.io/apps/contacts