So the campaign only having 3 missions available is a bug then?
No, it's only three missions. A beginning, middle and end. But there's been talk about trying to get the campagins from GC I and GC II added at some point so people could play them all at once. And there will always be more with expansions. And, who knows, maybe there will be DLC someday.
More to the point, when the mapping tools are (fully) released, there might very well be scenario support, which means people could, theoretically, make their own campaigns. Maybe. I think. Perhaps. All might depend on how much "scenario support" is ever released/made easy to implement.
Hmmm. Think I'll ask about this in the next devchat. Actually, during the modchat on Monday sounds like a good place to ask.