K/D ratio is required.
XP / hour is required.
Both are required to determine how useful a player is to the team.
A player (in this case, a medic) with K/D ratio of 2.0 and high XP / hour is a much greater asset than a player with low K/D ratio and high XP, or a player with high K/D and low XP / hour.
Simple.
Nonetheless, a Win/loss ratio for maps would be great too; which basically takes into account both of the above factors.