I wish everything worked like this. The reason it would be insane is it would be massively filled with x got a raise because he hangs out with y after work, y slept with so and so, w has a penis, z has big boobs, g was hired by h who sucks at negotiating, b completely oversold himself but wasn't bad enough at life to actually fire.

Good. Get those worms on the floor so you can stomp them out.

If the "you" in this situation never hears that they need to work on their code quality or their attitude, then they'll never know what needs to improve.

As a manager, it's my job to open those cans of worms. It's also my job to be continually helping people improve, so that issues like this never get to the "can of worms" stage.

Surely as a manager you understand that pitting people against each other is a recipe for disaster and not a path toward improvement.

In other words, never say "John's code is cleaner than yours", say "I suggest you work on polishing these pull requests".

I think there are plenty of ways to tell person A that they should learn from person B without pitting them against one another.

Normally I talk about this in terms of rubrics for roles and levels. E.g., it's not about Amy versus Betty; it's about how Amy can get from SWE 1 to SWE 2. In the course of that discussion I am totally willing to say, "Pay more attention to the code Betty submits for a code review. She's a solid SWE 2 and you could learn from the way she does X, Y, and Z."