The Zero Requiem only came up because the world was splintered and warring AFTER Lelouch managed to kill his father and thought his sister was dead. So basically, it was Lelouch's epilogue plan for the world. He'd already achieved one primary goal and failed the other. He decided to gather up all the hatred of the world into himself and then kill it to create a path to peace.
Eren's plan, on the other hand was "sure hope my friends stop me," *commence rumbling*
Lelouch had everything planned out to the last detail and it all went exactly as he predicted. Eren operated on what his future vision showed him was going to happen assuming he couldn't change anything and couldn't predict anything beyond his own death. Literally the only similar aspect between them is "I'll be the bad guy;" Lelouch intentionally set himself up to fail, Eren hoped he would but proceeded with the intent to succeed.
And Eren isn't a "worse" character because he's not a Lelouch-level genius, that's a bogus comparison. There aren't any characters like Lelouch in the AoT world and calling the rumbling a worse Zero Requiem and Eren a worse Lelouch is like saying a car is bad because you can't drive it across a lake. Your expectations were never fair to the car.