There were multiple evil people throughout the story and the author treated them all in light manner except for the mom's controller. The yandere big sis was also the same, until the author gave her the especially evil role (the one who nerfed MC all this time) just because the author needed a reason to boost MC's stats later. Even though he could have used other methods.
What's worse is that the author focused only on the bad part (the stats suppression) and ignored the good part (that she guaranteed MC's survival by constantly risking her life taking MC's injuries all this time, and just actually saved his life). Remember what MC did after he survived that lethal injury at floor 30? MC, spoiled by the big sis taking his injuries all this time, didn't show ANY gratitude and only showed anger towards the big sis.
That's why I don't like that part. That's just my personal opinion though.
Btw, MC's logic for why he blamed the big sis was WEIRD. "I am weak (despite lower-levelled MC being able to exhibit such an amazing athleticism at Erotic Bridge that all high-levelled adventurers there praised him). And yet recently my adventures went really well. Which made me wonder why. Maybe it's because I'm being helped by Philo and others buffed nerfed. But by what/who? I knew what it was when I was stopped from going into lower floor by chains (which was a really stupid move because none of adventurers there was strong enough; MC was basically just 1-hit killed; it's because he was spoiled by the big sis taking his injuries all this time). Chains = shackles = this chain must be what that shackled my stats! I know that the chain did more than just preventing me from going deeper. It also nerfed me! How do I know? It's a chain, a shackles; what more reason do you need? I'm sure of this. Imma go confront her now!"
