lawman
have another contact apps integrate with system db, other than default app which is quite useless.
I would use Tutanota's contact sync feature. It integrates well with native or third-party contacts app. However, you are now going to use the Tutanota app to add/delete/modify contacts details. Ask yourself if this is a deal breaker.
need a way to merge local vcf with google account contacts, but remove all duplicates.
Tutanota has a "merge" feature and ability export vcf for backups
then i can remove local contacts from default app, and just use google account - otherwise it shows duplicates in default app.
If duplicates show on the contacts app, try clearing cache and data from the contacts storage (the system app) and not in the contacts app
PS: I'm not shilling for Tutanota. I just found what works for me regarding contacts syncing.