I don't think I had trouble with that specific encounter by just fighting the boss instead of kiting, IIRC Hien does have some self-sustain, so you either didn't use it enough or weren't dodging the dodgeable things enough. The small number of skills is not very thrilling but I assume it's to avoid overwhelming players by suddenly dropping a full kit on them. Gameplay-wise these are hit or miss with people but I personally like having these fights from a story point of view.