Partially, yeah. Crewed spacecraft by necessity weigh significantly more than uncrewed, because life support is very heavy. But they also want to take that very heavy spacecraft further away from Earth than any crewed spacecraft has ever been before, which means they need to take a lot of fuel; yes, it’s a gravity-assisted free-return trajectory, but it still needs fuel for course corrections and other orbital dynamics. Plus, it’s a two-stage spacecraft, while the Saturn V was three-stage, so it’s got to carry a lot more dead weight a lot further than before.

All of that together means they needed the most powerful rocket ever. The lander mission will almost certainly be even more powerful than that, because while it won’t need to go as far, it’ll be carrying another spacecraft.