I calculated the stats if a LV 20 human ever entered the dark world, since in ch3 and 4 it's confirmed that your lightworld lv corresponds to your dark world level since the game lowers your light world health in fractions if you take damage in the dark world
>LV 20 human
>HP: 17000
>ATK: 38 (+ 16 with blackshard or twisted sword would be 54)
>DF: 4 (Kris and susies max no equipment DF is 2)
The ch4 titan has 21000 HP and 40 atk
The knight has 7300 and 40 atk (with sword equipped)
Spamton Neo, a powerful darkner, has 4809 hp and 13-26 atk
If you got to LV 21 somehow your hp would be ~22000, more than a freshly-hatched titan
You could easily solo a titan let alone the knight if you somehow kept your LV from a genocide route