Why I don't do DMG?

Hey! I followed the mekunas lighting spear build and it supposed to be the best build for sorcerer in this season.. but I don't do DMG.

I have all the maxed out gear (every piece have at least good 2 GA's), all the gems, maxed out witchcraft, all skill points and I'm currently on paragon 250.

I don't have expension, which doesn't allow me to put on runes... But are they really that important to do DMG? I literally do nothing to bosses on torment 4.