Fang Cheng's extra lives didn't amount to a piling-up of power. He could get over a hundred lives from a Legendary Great Demon, but that didn't mean the demon's strength was equal to that of a hundred Fang Chengs. Otherwise, if he got one extra life from an A-rank Monster, would that mean an A-rank Monster was as strong as Fang Cheng?
Although Fang Cheng's lives were called lives, they were actually currency belonging to the system, spent on upgrades and using cheats. Only resurrection was a system perk, and its cost never went up. That's why he could become an immortal.
So don't assume that losing dozens of lives means dozens of Fang Chengs died. In reality, it just means he spent dozens of units of the system's currency.
Also, my hints earlier were already quite clear: the Death Knight pays a price for using his mother's body. The tattoo on the back of his hand is that price, and it has quite a history. What he paid was far greater than what Fang Cheng paid.
I couldn't sleep at all last night. I lay down after lunch and only just woke up after my family called me. My head keeps throbbing, and it feels awful.
I'm taking the day off. I won't take any more days off this month, and I'll update as scheduled tomorrow.