Jeremy Irons is NOT LEX LUTHOR!?

Yeah, WB decided to cast Jeremy Irons in their Batman vs Superman but not quite Justice League of America movie. That is a good thing. Jeremy Irons is a great actor who has done wonderful work as evil masterminds like Scar or Simon Gruber, so he is PERFECT for Lex Luthor. Well, Scar is now Alfred...

Also... Zombieland's Jessie Eisenberg, AKA The Poor Man's Michael Cera, is now Lex Luthor.
Here's the thing: I saw the infamous Facebook movie and I get that Eisenberg could pull off a decent villain. Sadly he has more of a Harry Osborn Vibe than Lex Luthor...
I want to be excited about the movie. I was OK with Man-of-Steel... except the neckbreaking. Sadly, every bit of news I read I get more disappointed.

LEX FREAKING LUTHOR is how you step it up after ZOD!? REALLY!? You need Batman, Superman AND Wonder Woman to stop Lex Luthor!? Is he going to Steal forty cakes?

All jokes aside, how is Lex Luthor a greater threat than the Multiple Kryptonians that Superman fought in the first movie? He's a normal human without superpowers. (Intelligent, manipulative, but still a normal human) I know that I'm repeating myself, but isn't it a bit of an overkill to have a demigoddess, the last son of Krypton AND the god damned Batman to fight an evil Businessman/Scientist?

Again, I understand having these three against the immortal Vandal Savage, but not Lex Luthor. Now if Lex was playing second string to a bigger threat, THEN it could work.

Who is this threat? Vandal Savage? Darkseid? Mongul? Starro? Ares? Oh please don't tell me they're doing Doomsday...