You're making an assumption that they will negotiate your pay up, and not correct the under performers down, or do neither. More data is useful yes, but not on a per-employee basis. If the average for your position is higher, then yes, you can use that, but if it's an individual you're unlikely to get any difference for yourself, but could negatively impact them.
Having more data in a negotiation is never a bad thing, having less always is.