First, there's no levels 10-12. Just level nine. Second, Gillard came up with this based on Lucas's assertions about Palpatine, Mace, Yoda and Anakin. That only Mace and Yoda could compete with Palpatine in battle and that Anakin could destroy Sidious. Gillard made it easier by giving us numbers. The Jedi reach level eight, which is pretty much the limit for all of them. They can reach level nine, but it's difficult and takes time. Yoda and Mace pulled it off without turning. Sidious is the Dark Lord of the Sith. Anakin makes the jump to level nine, but he cannot handle the power and it goes to his head. Especially when he turns and fights Obi-wan, who uses his anger and arrogance against him. Against Palpatine, he wouldn't last as long as Palpatine's much more refined in his fighting ability. He's less prone to making mistakes and loosing control of his anger.