I don't think KDR should be factored in. The only fitting way I see including deaths is if the player had used resources prior to death. For instance, buying a shotgun and getting eaten by skulks or evolving gorge and getting killed in some fashion. Most rewards in terms of ranking should come from destroying structures and killing people who bought things with resources (jetpacks, exos, onos, fade....). I feel this way would encourage players to take more risks and not worry about the negative effects of dying and rewarding the lone marine who flew into the hive to destroy their upgrades.

My 2 cents.