Now... let's see how he can circumvent the chant.
...or maybe he'll just copy her magic. Megaman it up!
Basically what I'm assuming. When she talks about lineage, she says their family's founder used a "widely used True Ancestor Magic", which is what passes magic down through generations. If this applies to magic itself, and not just incantations, it would explain how the 107 families consolidate actual magic power (like the swordsmen), but with the important detail being that if you could somehow use the family's True Ancestor Magic, you'd be able to tap into their magical power too (if that's how it works).
So, if Durandal figures out what to look at for the "true ancestor magic", he'll be able to hijack the spells she casts, but also potentially the family's magic power, which would explain a way he could actually power up enough to defeat the other 106 mages (by just collecting tons of familys' worth of magic power)