Thank you Krono for a well thought out post. Was afraid I would have to do all that work.
Also, for the people claiming this was a one-slash fight, did you guys really forget that this fight has technically been going for 5 chapters now? It started in 311 and ended in 315, just because Minerva came and left doesn't suddenly make this an entirely different fight.
Also, Kagura was hardly portrayed as weak, she held her own throughout the fight and even had the advantage last chapter. In this chapter she displayed a rather staggering amount of power by cutting through the Arena's magic barrier (a feat only Minerva and Natsu have matched), then the Arena, then through the entire city (which exceeds any prior example). It is probably the single strongest attack we have witnessed in this arc so far. Just because she ended up losing the fight doesn't make her weak.
Erza didn't even try blocking it head on, she deflected it. Then she simply struck before Kagura when she attempted to attack again.