Overlord_Venus
I theorise the Readon why grade Four Sytems can't enter the Fray is due and aspect of the Plot Phenomenon of Plot Device Balance. To simply this part refers to the fact that in a novel everything must be balanced at the level fo the story and anything beyond that Must be Nerfed until the power scale reaches there. E.G. if the Protagonist is at the beginning of the story even if they kill the son of this god like enemy either the enemy won't find out yet, or they can't descend to that place or some one time power held them off from attacking or maybe they have some relation to the protag but no matter what the plot will never allow that enemy to face the MC in fair grounds simply because in a fair fight the MC would simply die. Only when MC is strong enough or has the means to deal with them will they be allowed to appear so either the MC is an OP mc from the start or they have some cheat to get them started. so perhaps the momment grade four systems descend the will of the previous MC will awaken and Do something since its power is the power of tropes and clichés. or Maybe they're just weakened and recovering too
u wonder where the main character system came from, since it's another world I imagine the nature of said world is parasitic and latched in the strongest world it could find (the system world) and either stole its energy to make a system or created a replica of its own similar to the reality marble that birthed the dragon of systems. with a whole world focusing to create a whole entity (and maybe the system world too used its energy for that) they are bound to be incredibly powerful. I guess we'll see