I agree PR in private company is slow. But imagine for any large scale production system that used by million users. A careless bug without spotted can cost a company million dollars. To speed up code review the only way is the combination of what you stated: TDD, CI, Pair Programming. After that a review from senior engineer can focus on the tests and any malicous pattern. The distrust is needed sometimes, especially when you work with a global remote team with diverse culture and skill sets.