Just trying not so confuse realistic testing with self-deception :) Not convinced testing with synthetic data can pretend to be similar to a production environment.

It is not realistic to replicate a production setup in development when you’re working with sensitive user data. I’ve worked in different contexts (law enforcement, healthcare, financial services) where we’ve had complicated setups (in one instance including a thing called pre-staging environment), but never would a sizeable team of developers have access to user data, and thus to a realistic setup in terms of size, let alone of quality of data.