Luthor seemed to have the situation handled, but Lex took a tour of the area on his own anyway. Truth be told, he currently had a much easier alternative to solving this issue. He could use his authority to seal the Minor realm up. But in the event that some other Minor realm invaded later on, he would not be able to do the same.
That is why it was best to set a precedent beforehand for handling such issues themselves.
Lex took some of the weapons that were being used by the invaders, who were a race that identified themselves as Berkin. The weapons were guns that looked like they had come out of a scifi movie or video game. He shot a few rounds and was impressed by the super heated bullets.