This is why i love mc like this, they are not strong because they have overwhelming strength or godlike techniques...they are strong because they can beat strong people, as simple as that. In the novel, his fight with the hero Oliver is more detailed. Oliver who had a strong magical capabilities and overwhelming strength vs Cid who can't even use mana(no mana=normal physical strength) in a sense it was like a fight between hulk and an average human in physical sense. It should be impossible to beat her in that state, but he did ,not because of his overpowered strength but because he
willed to beat her. Don't get me wrong, im not saying that his "will" alone is sufficient to defeat her, but im saying that its the biggest factor. He was determined to beat her by sacrificing his body and biting his neck off. If he doesnt have his sword, he will use his nails,if his nail were ripped apart, he will use his teeth, if his teeth has fallen, he will use his bone... Thats is the reason why he was strong. And its the most realistic thing that i have seen in manga and novels. Just read the novel for a clearer explaination. He kinda reminds me of Lee Ho Jae from The tutorial is too hard.
https://tenshihonyakusha.wordpress.com/to-be-a-power-in-the-shadows/power-shadow-ch-059/ Chapter 59 for those who are curious...