This scenario would work fine if we weren't limited to the city control points because what's the point of being able to get a city from somebody when you cannot have it due to the lack of city control points?
On the other hand, had the city control point system been eliminated, then, as
jkljosiah rightly pointed out, stronger players would be beating weaker ones out of their towns - to be honest, and not to make too much of myself, I'd be among the first to do this
Then again, there's little difference between beating someone out of his/her towns and beating someone's towns into porks.