Theories on the new episodes?

(SPOILER ALERT!) So after watching the new episodes, I don't really see any problems with the whole plot except for the "exotic matter" thing. I have two theories, the logical one is that the exotic matter was formed when El opened the wormhole, keeping the walls of the wormhole intact, and Brenner just studied it. But the way the show explains it is that the exotic matter was "created" by Brenner. If that were to be true then how were the walls even able to exist without it? How was the upside down even a thing if it was supposed to be sucked out into the void. Because Brenner couldn't have "made" the exotic matter before the upside down was even created.