Lex's master plan was kinda weak. I mean, if the plot was aimed at younger kids... sure it would be fine. Or if Lex wanted to destroy the world just because he's evil, sure it would be fine.
But here, his actions did not rationally match up with his ideas.
The crystal was eventually going to make a continent that would destroy most of North America... along with LARGE chunks of Africa and South America according to Lex's maps. Plus, the effects on ocean levels... climate... the atmosphere... it's no wonder he believed that billions would die.
Yet his GOAL was to create land that he owned alone and then sell it.
First off, no government on Earth would recognize Lex as having the right to own that land. If you kill billions of people, governments are gonna come after you. Not cater to you.
Secondly, if Lex destroys nations and crashes the world's economy... who is going to be able to buy his land even if we suppose that he'd actually be able to control all that land.
Third, the US military would wipe him out. A decent amount of time went by, and that island still hadn't grown enough to do more than give Metropolis an earthquake. The military would have plenty of time to bomb the crap out of that island or even just storm it and capture Luthor. Luthor had no Kryptonian weapons. We don't even know if he knew how to build them yet. Or how long building them would take. Plus, he only had three guys with him. Even if the weapons popped out quick, three guys vs. hundreds of thousand of US soldiers??? Numbers will win out even if the weapons are uber powerful.
Fourth, if all went to plan and the continent grew... people will be swarming all over that new continent in order to seek a place to live. How was Lex planning on monitoring his borders for an entire continent... with just THREE guys and himself? Advanced alien border protection? lol
Imagine if the United States was completely barren except for 4 guys with some insanely powerful guns. Now imagine millions of people trying to get onto the US coming from Mexico, Canada, and over the sea. The 4 guys would never stop them all. Nor would the 4 guys have any way to regulate or control all those people.
So Lex's plan fails on almost every level of planning. Which is sad since he's supposed to be a genius.
For anyone saying "Oh, Spider-Man's villains plans were dumb too!"... what are you talking about?
Green Goblin wanted to kill off the people trying to take his company away. And he did by using his secret ID. And guess what? His plan worked. After that, he just started to go completely insane and wanted to murder people who challenged him. So he does all sorts of crazy stuff to piss off Spidey and try to kill him.
Doc Ock was simply 100% insane after the artificial intelligence in his mechanized arms took over. He really had NO plan at all other than trying to get money to finish his plan for controlled fusion (an obsession that the arms fed into). Crazy plan for a totally insane guy.
Lex doesn't get the luxury of being totally insane like Doc Ock... mostly because he's supposed to be a criminal genius. Up until his "real estate plan", everything he did was logical and calculated and worked.
Then he just whips out a scheme that a totally insane person would use, but he's supposed to be doing it for logical reasons.
And oddly enough, even insane Doc Ock's plans worked out. He managed to get all the money and material he needed to finish his project. Only after getting knocked around and gaining control over his arms did he realize his plan was insane/fruitless and put a stop to it.
But if Lex's plan had gone through... even the way he wanted it... it would have failed. Hence, his master plan is craptacular.