[sciencenerd]

I can't speak for everybody, but team 1318 dismissed the catapult idea early in our first brainstorming meeting as hard to reload, hard to make accurate, hard to shield, and hard to make as powerful as necessary. I will be very impressed with any team that pulls this off successfully.

And I'm not sure what you mean by "hard to defend". I don't see how it would be harder to defend against a catapult design than any other type. And of course, breaking the arm off would be against the rules, so that isn't a legitimate strategy.