All of Apple's first-party services give detailed breakdowns of what information Apple receives before it does so. Other than privately-stored iCloud data, they send virtually zero non-anonymized data to Apple. And as much as possible - especially with things like Maps - they keep data local to your device.
So no, I don't always know who third-party apps are contacting, because nobody can. But I do know (and have control over) every interaction they have with the rest of my device and data. For first-party apps, I do know everyone they contact and with what information, and it's kept to a reasonable minimum.