My guess is that the best player of one week will become Paragon for next one and so could be the one to decide the Paragon Defense. Because he’s considered the best player of the guild, one can assume that he will choose the most difficult team… And the same for all the members according to their Guild War Rank. Or maybe I’m wrong ;-). In fact, I prefer to be wrong…
But just an “increase of the stats” is meh. Because it will look like Challenge mode: 5 times the same fight… And also we don’t know yet if we will have Scout in Guild War (can be drastically increase the difficulty). If not, it’s just impossible to have the same fight at the different Guild War rank…