How does one not process-gate something like PR reviews? Example: several times we've had mid-level devs do work in code that could have been handled by a lang

How does one not process-gate something like PR reviews? Example: several times we've had mid-level devs do work in code that could have been handled by a language function, or built out a portion of the system without thinking about how it impacts another portion, or doing work without writing tests... all things that we've attempted to stress to everyone on the team repeatedly. Other mid-level team members who are already performing reviews aren't calling out these things, so the only thing that seems to work is adding a process-gate where some of the more senior team members are required to approve. I hate it, but nothing else has seemed to work.