So is it just me or is Apple’s Contacts app just terrible? It seems that it hasn’t been touched in years and when I try to do simple things like add a group, it doesn’t seem to work. Exporting is only available via Vcard… etc. Can you use a different contact manager and have it become the central player in mail and such?
asking for a friend. 
I use BusyContacts but I cannot tell you if it’s better than Apple’s Contacts. I’m not a heavy contact management user.
After using various CRM programs including the amazingly powerful C•A•T (Contacts, Activities, Time) by Chang Labs in the 90’s, I switched to BusyContacts (and BusyCal) about 8 years ago and have never looked back. Apple Mail shows in each contacts “Activity” feed which includes past and future events from BusyCal, tasks and tweets. All kept in sync with dedicated iOS BusyCal and Contacts app on iPhone and iPad. I think it is worth a look for any Mac/iOS user seeking steps up from Contacts and Calendar. 
Does it share with family members?
David
I am still using the Apple app, because I tried a third-party one about 18 months ago, and it inserted a birthday of February 1, 1601 for every contact.
Me too, and agreed.