When a product owner starts explaining why the team needs code reviews, instead of the team, that's when you know that the organization is fucked up and business people are the ones setting up checks and gateways for "quality assurance" .. Sure, you need code reviews when 90% of the developers don't even know what automated tests are. Hopeless morons!

Code reviews are always a good thing and best combined with unit tests.

I would not say one replaced the other.

Unit tests protects against regression but does nothing for readability or to keep the code maintainable.

Even bad code can compile and pass tests but might be very hard to read and understand and require complete rewrites to add new functionality.

Also, code reviews is a perfect opportunity to share knowledge of the code so more people have seen each piece of code.

We use both always.