I think you're missing the point of code review. By the time when the PR is ready to merge, discussions around the architecture and how the code should be structured should already be part of the tech design of a given feature. So the discussion around whether a A feature is built and planned in a maintainable way, should be way before a PR is filed. A PR review is making sure that you verify against the already agreed-upon structure, making sure everything matches the plan, and also find bugs and stuff that was missed, according to the plan.