I understand MC's genocide route. Quality over quantity is the rule of thumb for deck building. They can only draw once a day, why waste it on trash? 
The problem lies in MC's predicament. MC is bound to come up against various deck builds which means that he/she will inevitably face opponents that are to his/her disadvantage. I think the right call here is versatility over speciality. Having a versatile deck that can counter anything seems like the best decision. Especially seeing as how the world works where the game is perpetual. 
(When MC said that he/she'll die when she runs out of cards to draw, I think she was worried of facing a mill deck)