My experience on Phinigel was that good groups relied heavily on ENC charm; only shit groups really needed a tank... it was more about being a badass puller who can deal with overcrowded zones and keep their group fed with kills. That being said, with the way AC is overpowered on these servers, I'm pretty sure a Ranger has no problem tanking if need be. Its just that... why not have the ENC pet tank?
edit: friends have mentioned Ranger is nice in that they can farm Quillmane and Rathe Mountain names, too.