Instead of updating one entity, you will need to update every single object that contains the wrong data.
No, this is not true. Your invoice has a reference to the vendor. If you update that vendor object, when you request the invoice, you'll get the updated vendor object.
Your complaint describes problems associated with document databases. Document databases are not object databases. (For example, CouchDB is a document database, not an object database. So if you hate CouchDB, you might not hate object databases.)
Do you know what happens if one those entities change, like a phone number, a vendor's email or a product packaging?
Instead of updating one entity, you will need to update every single object that contains the wrong data.
How do you maintain integrity if redundancy is part of your model?