User blog comment:B214/Talk About What You Want! 2/@comment-24409634-20140628103520/@comment-16281343-20140628123309

Just like what B said, the only redeeming quality of Ascalon is its Dragon-slaying ability. Its trait as a holy sword isn't that great compared to Durandal and Excalibur.

But in the hands of Issei, he can boost those two with his SG. Issei doesn't have any background in martial arts. All that he knows are through experience and some coaching from his teammates.

So, he cannot use Ascalon as a sword but he was able to use the abilities of Ascalon and infuse it in his attacks (not just his punches).

~All in all, Ascalon isn't wasted on him since he can still use the traits of the sword.