Pyron_Knight
Eater of Worlds
As she is the last sorceress of her time she has all of the sorceress power there ever was. She was taking power from all the other sorceresses because she had the entire sorceress half of the great hyne and manipulated the other sorceresses to change time and cause time compression. It doesn't say she was trying to take their power, it says she already had it and was trying to change time.
I don't see how your interpretation makes no sense.
First part:
A sorceress trying to change the world by compressing time
^ establishes she's trying to do something ie. it's not done yet and she has to accomplish it.
AND
^ establishes a link. There is another thing she hasn't done yet and is trying to do.
aking power from all sorceresses.
^ there you go. If your interpretation was right and she had it already it would not say very clearly that she was trying to take power from all soreresses.
And how does Kuja win Well for one Ultimecia has almost no feats in her regular form. The best you can guess at is she can do whatever Edea did and more but that's about it. And blocking bullets and chucking ice isn't comparable to smiling off Bahamut's attacks.