Nice, so they are hot takes :D

If the design of a code change is bad, noticing that in the PR stage is not desirable. It should be discussed before someone actually went ahead and implemented it. It can also happen if people misunderstand the architecture, but again, that should be cleared up before actually implementing a change. Code style should be enforced automatically, as should test coverage and performance. Code review is also pretty bad at finding bugs from my experience. That imo leaves very few things where code review is useful that are not nitpicking.

As for programming languages, the amount does matter for individuals and for teams/organisations. A developer who can only use a single language is not very good, and using a many different languages within the same team is not good either.