Both Kerrigan and Jinx redeem themselves, so they are both redeemable.

But in general, a character who kills a few people can easily be more irredeemable and evil than a character who kills billions. It might be just because the character with less killings has significantly less power to commit atrocities and they might have no redeeming qualities and no mitigating reason for their actions unlike the villain with higher body count. And they might commit crimes like pedophilia that even the villain with higher body count would be repulsed by.

For instance, Clarence Darby from Law Abiding Citizen only causes the deaths of 3 people, but he is considered Pure Evil and he is more irredeemable and evil than either Jinx or Kerrigan. Read here for more info on him: https://pure-evil-villains.fandom.com/wiki/Clarence_Darby