An elaborate plan; of course, they needed an elaborate plan. They weren't just killing a beast like what Noah thought. Those memories contained Montana Mills's visit to the Pandemonium itself. The child had been to the clusters and had seen the defenses of the beast. Killing the Heart was only a phase of the plan.
Not only was Noah the type who would endure a little sneaking as long as the results were in his favor, but he was also the type who didn't want to do everything by himself. Even with that power he had, he could grow lazy if he was not fighting something. He might be jumping into action, but he wouldn't want to sit through a plan filled with a lot of precaution.
That was why Sagan and the rest had to do it. The only danger in their plan was that, if they had a mishap, Noah might need to save more people that he couldn't afford to lose.
