Trying to parse your sentence, which is ambiguous...
You're saying that the manager-of-managers would argue that the number of PRs should affect perf ratings? Or the MoM would push back against the line managers who were giving ratings based on # of PRs?
They were reviewing perf designations, then pulling up PR count, then arguing against designation based on the number of PRs opened.
That still doesn't clarify: were they saying "many PRs→good" or "many PRs→bad" or "number of PRs is irrelevant" or...?
That PRs == impact.