Cordelia -Attack +Speed

Just know you're not alone. I too have had my unfair share of unusable IV units. I actually have a Hinoka with the same IVs as your Cordelia. But you make the most of what you've got. If you like a character, by all means use them.

Running Life and Death + Luna should patch it up slightly if you're intent on using her. I really love Cordelia but that -3 atk does reduce her viability but her SPD should be her saving grace since the final hit, should she quad attack, will be able to take out most reds and blue's. Also, I suggest using a Hone Atk buffer or better yet, Delthea so she could reach her full potential! Condolences by the way!

Bad IVs are very common, in the Bridal banner I Get a B.Caeda with -Atk +Def the worst IV combination... twice!!.
I leveled and used just because i liked the character, at least work like a normal blue mage.