Lex in this movie is based off the young Lex Luthor character thats found in Superman Birthright. The producers have already said that Lex will grow over multiple movies becoming the Lex that everyone knows. This is the beginning point for him and in a lot of ways for Superman as well as a new beginning for Bruce. DCEU wants to show these characters stumble and fall before becoming fully formed, i find it to be a very interesting journey to be a part of.