I think Skyy has a good point and optional pets might take us right back into the GW1 mold for rangers. If pets are not required, then perhaps they should not exist as anything more than a temporary summons (such as the birds called by a ranger with a warhorn) and rangers should have been given a different professional mechanic.
As for the viability of fire-only eles, I think I would hate to be on a team with one. If your group is under heavy pressure and a quick Geyser or Healing Rain could pull you through, would you accept the ele telling you after the wipe that he's a fire ele and it's unreasonable of you to expect him to ever do anything else, even if the necessary skills are only an attunement-switch away?
I don't really see how an ele is rewarded any more for traiting two or three skills in one element than by spreading traits across elements or using generic traits. It depends on the play style, and a flexible approach should work at least as well as an approach focusing on one element. Each element has its own trait line, so only the weapon traits require decisions between generic and skill-specific traits. Is an ele with, say, improved Fireball and Lava Font really that much better off than one who improves Static Field and stuns his foes before switching to blast them with an improved Fireball?