The Zolo encounter is not trivial. That event for the level it is intended can be quite difficult if the skeleton totem is not contained quickly.

Furthermore, not all 70 classes can efficiently take advantage of that design flaw. It was specific enough that Blizzard did not bother with it for some time until some video of it was posted.

The side benefit of this was the exp gains were really fast. Blizzard removed that side benefit and left the encounter as is.

There was no "exploit" that violated the ToS--it's the same encounter even after the exp nerf. There is no bug in the encounter, it's an intended mini boss fight.