That's the problem. The system wants to assign one number to performance and fire based on that yet even getting an approximation of that is hard > Someone who

That's the problem. The system wants to assign one number to performance and fire based on that yet even getting an approximation of that is hard > Someone who closes out tons of tickets but is a complete asshole and hated by their teammates should get a worse performance review than someone who codes less but provides mentorship and guidance and is generally pleasant to work with. They should get a talk with their manager about the attitude and if they don't fix it they should be fired; not wait for any ranking to cull them.