I think we are normalizing the PR process here, in reality its more convoluted and a good reflection of the team/organization itself. The relationship between the author and reviewer can have negative impact on the rationale and desired outcome of the PR itself.

To run the process smoothly, one can just hope that the team/tech lead is an ideal developer. Otherwise they are in a position where no one senior than them is available for the code review and any one junior would just rubber stamp their PR's.