
Sage's plan actually make sense with what we know of her character
I think Sage always hated humanity for her Grandma's death, belittling her, and beyond. She's considered the smartest person in the world, but Gen V showed she's not above cognitive dissonance when it comes to her emotional biases. She probably hates how human she is when it comes to her own emotions.
Destroying humanity and Supes as a whole just fits in my opinion. She'll sacrifice anything, even her beloved taco bell, to achieve this. Humans are animals is something she's believed since her debut. I don't know why so many doubt this is her actual plan. Her disdain has been blunt since the beginning.