The Regressed Demon Lord is Kind회귀한 마왕은 착하게 산다

idk about now, but when I first read this (at that time ~300 was the latest chapter and still ongoing), this was the top novel (both in rating and discussed) in wuxiaworld and many aggregators.

Well, I think the total "power level" of someone can be divided into,

1. Innate mana capacity - This is the total mana a human can possibly use, like a max limit. It's decided at birth. Everyone starts with their mana "locked" and when they awaken mana, they can train it bit by bit to "unlock" more and they reach a limit that is this "Innate mana capacity ". There are some ways to increase this limit but those are spoilers. Also the larger the mana capacity, the longer it takes to awaken (like MC).
A rough reference of mana capacity can be seen as,
Godlike entities > Dragons > Elves > Humans. I know there maybe more but idr. Our MC has a mana limit of dragons, and he unlocks it quite fast by using risky methods (minor spoilers maybe).

2. Physical body - This is much like in real life. You exercise to gain strength. MC starts with a weak body but gradually improves along the story.

3. Techniques/spells - These are "skills" that individuals create much like various martial arts techniques in real life. Warriors usually infuse mana into their body and weapon according to the method they invented or inherited. Mages use spells instead of techniques where mana is infused into models and visualizing bla bla bla... you know, the usual fantasy stuff.
MC already has many techniques he invented in his past life. They're all OP.

4. Weapons - Weapons, depending on the material used to make them, has certain mana conductivity. More conductivity = more boost. The 3 named swords are the best in the world. For reference,

Afaik, the power level of someone is based on those 4 factors.

(sorry for the late reply, i dont get notified for some unknown reason when someone replies to me)