While ilvl give you a good idea on stats to have to run the dungeon it is only a bare minimum requirement to participate. What determines the run is communication and player experience with their role. This what many players who are blinded by stats and expectations of others fail to understand. Tanks should keep in mind what they can pull and not feel pressured, should be able to gauge their party DPS on a first pull, and keep in mind the healer or at a minimum ask how comfortable they feel with speed runs. Healers should at a minimum able to speak up. Increasing ilvl requirements would really not make much of a difference, you can't teach experience to person who thinks they know their role.