A code review is an engineering practice and a knowledge management process; it should not be confused with a merge or pull request, which is a change management and version control process. When you say, “code review wasn’t even ubiquitous until around 2012–2014…,” I think you’re referring to the approval tooling built into merge requests, not to code review itself. Engineers were having their code reviewed long before then.

By the time you genuinely expect a PR to be merged, it should be essentially rubber-stampable, in my opinion. It shouldn’t be the first time someone else is looking at your code—let alone the first time anyone is reviewing your design.