Source: Blizzard GuruYeah, I think you guys hit the nail.
We’re setting out to create unique, interesting, and diverse classes that each have their own style and flavor. Most importantly this isn’t just a basic look at each individual class, but how they compare to each other and overlap (or hopefully, don’t).
When you up the number of classes more and more you’re eventually going to begin down the route of homogenization, they start to bleed into each other’s core abilities and styles which really just detracts from each individual class’ recognizability and distinction within the game.
In addition, by limiting the number - and I say limiting not because it’s a low number, it’s the number of classes in Diablo II and a good one at that, but because we’re not going crazy with it - we can focus on making each class really impressive, both visually and through the way they each feel and play.