The game can be hard as it can be easy, it depends whether or not you understand the tatics that make this game simple, or not.
In my opinion, games tend to become harder (require skill) when you are limited by time to perform your actions, so I view D:OS as quite simple. D:OS requires understanding, and perhaps some preparation, but not much skill.
A man-at-arms tank kinda sucks, but not to the point of making the game impossible.
What builds have you tested up until now? You mention 20.
