It is utterly over-complicated compared to vb3 - especially when managing moderators.
There are your usergroup permissions and your individual user permissions, but that isn't enough - you still have to manually set each one as a moderator - and then individually set up each one's individual moderator permissions.
Even then, although you can set moderators to "ban" using the spam cleaner, you cannot set moderators to simply "ban" without using the spam cleaner!
Xenforo does a lot of things really well, and almost everything else sleek and simple as required. But the whole permissions system has a logic that only a programmer could love.