I don't know that what you are saying is true. When I first started playing GvG, I was told by a Top 10 player who was our guild's Founder, that the city attack/defense boosts that one normally relies upon when attacking are not relevant to GvG battles. In effect, they are worthless in GvG. And to me, this makes sense. My city was much weaker then, and I still was able to play GvG effectively because I was in a very strong guild with plenty of support pool. But, I do hear people say, like yourself, Dursland, that attack/defense boosts do factor into GvG fights. I'm wondering if anyone can cite any supporting evidence, either way, besides merely asserting that it is so or speculating on the logic of the support pool and support factor system and experience fighting in GvG.
In other battles, for example in Battlegrounds, one can see the strength of one's military units, as well as the strength of the defenders. In GvG, this is not the case. All one knows is the support pool bonus of the defenders.
I don't think that I have ever fought a manual battle in GvG. Maybe one can see something there?
So, the question still remains, how is the relative strength of an attacking army and a defending army determined?