Don't think you should think of it as a rpg kind of game, with stats and lvl. More like some fighting game. Alicia and Fate mentioned that the cards defined the basis of their avatar and skill set, but it was up to the player to define how to use them.
Another thing to keep in mind is for now, the girls never battled against Dark Material with their full line-up. It was always an incomplete roster with some chivits. As for the chivits actual skills, we didn't see much about it either, as we mostly seen the levi based one (3 of them trying to do the exact same thing) and the ouchama, who mostly stayed in the back and let the player act. And in each cases, it was a close win from T&H.
And the prof's daughters doesn't seem to be taking part in the ranking, so I suppose that being the prof's daughter, they might have overpowered avatar with the best skills out there, kinda like some debug mode. Might have way more experience than even the DMs if they tested it since early developement stage.
I was more surprised by Fate not doing too well, but then again, they mentioned she was somewhat holding back to keep on level with Arisa and Suzuka.
As power balance goes in battle manga, I've seen way worse.
