Why isn't level 8 interesting? I think it's very interesting. And in general, the more levels, the more interesting it is.
In general, the issue isn't just the imbalance. There won't be 8 levels in HotA because the developers are trying to minimize the similarities with In the Wake of Gods.
And that's a good thing; I want to see an add-on to Shades of Darkness, not a mod for In the Wake of Gods.