First of all, the SuperDracos were designed from the start primarily as a launch escape system. Although using them for propulsive landing was explored extensively, it was never implemented.
For landing on Earth or Mars, the atmosphere is used to lose most of the craft's speed, with the thrusters (and/or parachute) used only after that. The moon has no atmosphere so the entire landing process must be propulsive, which would require a sustained burn (and a lot of only moderately-efficient propellant) that SuperDracos weren't designed for. Maybe they could take it as is, but I wouldn't count on it.
SuperDracos aren't actually very powerful compared to a booster's main engines. A Falcon 9 coming in for landing uses 1-3 of its Merlin 1D engines, each of which are 1.5x as powerful as all 8 SuperDracos on a Dragon2. Landing a Starship even on the moon is likely going to require even more power, due to the high "dry mass" of the craft, the return fuel it might be carrying, and the payload it will be carrying. With enough SuperDracos it could probably be done, but that seems silly compared to just using a few more-powerful landing engines.