It is just my impression, but I think what Elis thoughts were actually suppossed to hint at is that he noticed that Edna only used weapons she had to use because she had nothing else or the situation just didn't allow her to only go for single sword fighting, because dual may have been the more efficient style in that situation.
Meaning he never truly knew her true strength and totally underestimated her true skills, because she never really had the opportunity to show off her skills in single sword fight where her true skills and strength lie.
Buuuuuuut could also be just my wishful thinking, cause having a fl thats as cute as Edna but also strong decisive and badass being stronger than our normally almighty hero ml is just too nice~ ヾ(☆▽☆)
Omg I think you’re right! Thanks (^○^)
I think what he said means that she isn't even using her weapon of choice, and with that acknowledging how strong she really is. She beat him with weapon he prefers, imagine what she could do using what she's more comfortable with :)
You gotta master one sword before you can use two and her mother made her pick up the whip refer to chap 63
Like Eli said Edna used a whip and double swords so how did she become so good with the sword? Was the whip just something she wanted?