Part of the idea behind this game was that every encounter could be beat regardless of party setup, as long as you have the standard tank, dps, heals thing going on, if they were going to have to make a mechanic for ranged, and a mechanic for melee, then why not just do what they did, and have the same mechanic affect both, it's just as easy to dodge weight as melee as it is ranged, the only time it can get troublesome is if everyone is loosely spread out so everyone runs into other people's plumes, and that is just poor playing, not poor mechanics. The fights are group fights, you need to be able to do your individual thing well, while working in a group, if someone messes up, and you get killed, then that is fine, teach them, or replace them. As for some mechanics affecting melee and not ranged, the only one I can think of right of is Ifrit, and Sear or Vulcan blast isn't going to get you killed, its more of a healer mechanic, to keep them busy, and vulcan blast is sort of bothersome for ranged, you have to stay back or you get interrupted, making you have to move more during plumes than melee.