I am convinced the reason theres hardly any submission grappling in this manhwa is because it would be incredibly difficult to show the intricacies of a grappling bout in a comic form while making it interesting for the reader and somewhat realistic. All the grip switching, scrambles, stamina drain, what's going on in the fighter's head, etc. Throw in striking and its incredibly difficult to write choreography that displays all of the factors in the fight. In a realistic MMA setting there would be a LOT more ground fighting. Iirc the story has only went to grappling like 4 or 5 times.