I just think that, in order to do Lex Luthor correctly, he needs to have an arc. From self-appointed savior of metropolis genius businessman, to half-crazed, Superman-hating Kryptonite wielding villain.
You set Lex up for that in this movie by him instantly mistrusting Superman, out of jealousy or fear or what have you(preferably jealousy, it's more interesting). So you have him create Metallo for protection. Like in the animated series sort of.
Metallo goes rogue, tries to outright kill Superman publicly, Superman defeats him, learns that Lex was responsible(preferably from Batman's investigations into LexCorp), but can't prove that he was, and you've instantly set up the hatred between Superman and Lex perfectly.
That way you have the action and physically dangerous villain threat, but also the finally done correctly Lex and the underlying threat Lex presents.
And you get an interesting dynamic of a guy like John Corben talking to Superman with his chest open revealing his Kryptonite heart as he's punching Superman around.