Originally Posted by
Rikuto-san
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Defense penetration will only remove another players defense stat and take it down to 0%, never below that. "smart" high gear builds put the defense stat close to 0% anyway, because it potentially wastes their opponents penetration stat while allowing them to boost their other stats as a tradeoff.
So basically, defense penetration is useful against certain players who don't know any better, but attack is always good regardless of who you are fighting.