My point was that the scope/impact/value/etc of the contributions made by individual engineers will be determined more by the projects they're working on than by their inherent ability to contribute. So, if we go through the org and cut the bottom 5% of engineers by how much value they added to the company, most cuts will be determined by the context in which an individual was operating rather than their inherent ability to contribute. Ie, the cuts will mostly just punish people for getting stuck with bad managers or lackluster projects.
Of course, some people are obviously great in any context and some are obviously useless (or worse) in any context, but those folks should already be handled appropriately even without the "cut 5%" mandate.