User blog comment:Crimson and Darkness/Volume 25 discussion blog/@comment-33939194-20180515104156/@comment-28884330-20180515223512

Issei didn't defeat Vidar through raw power, though. He was not stronger than Vidar with the Midgardsormr armor, and defeated him through smart use of the dragon slayer qualities of both Ascalons + Penetrate, turning the dragon armor's weakness into his win.