Genocide isn't about giving you a challenge. If you've gotten to NEO, then you might have picked up on some anti-completionist tones.
It doesn't assume you're doing what you are because you're evil, but that you're a powerplayer. You're grinding the soul out of the game; it only makes sense for nearly everything in it to be a pushover.
Undyne the Undying is the biggest nod to the villainous role that your playing habit puts you in, in the game's eyes, but the rest is about that sense of soullessness.