Omega's Light Form:It is stronger depending on the amount of good in Omega.So since Shadow Omega is not only UNNATURAL but negative as well,this form is actually far weaker than it could be.This is his equivalent of Super Saiyan Blue or Super Saiyan Ikari/Super Saiyan Rage(Trunks' form).If Shadow Omega wasn't a thing it would be like a Potenial Unleashed SSB form.

Dark's Nega-Mode:This form gets stronger depending on the user's want to kill.Since Dark usually holds back on most weaker opponents,this form is as restrained as Omega's Light Form.

Arko's Weird-Looking Forms:He has some very mutated blood and that's why his forms look so weird XD