Really need to add more mobs. Sometimes a group of them will spawn, but when you have likely now 630 (at minimum) players rushing around a relatively large, but small for the number of players, area, bursting down mobs with an objective bar that is tracked on a per player contribution, not an overall contribution, it becomes a bit of a frustrating mess.
One of the issues I’ve seen is that the Nightfall event rewards classes/races with built-in mobility. Evokers/Dracthyrs, Paladins, Monks, Priests to a lesser degree, and so on. If you don’t have speed, you have to rely on mounting up and down, and given how quickly enemies can be burst down, it can be a bit of a frustrating experience.