Elementalist has been widely promoted as being very flexible, while reports on the engineer seem rife with reports of randomness poor turret AU etc. I wonder if such reports have influenced people's choices.
IMO in the current state Engi, Necro, Mesmer and Thief are all pretty niche to the point of redundancy. For 90% of average/casual players, anyway. The skillcurves involved do not give any real payoff to most people.

