It's not just the landing, that's relatively simple and can be mostly done with bigger thrusters on the craft but you have to slow down a lot before you can safely. Right now that's done through a heat shield then a parachute and finally the actual propulsive landing of the SkyCrane. We've done some testing of inflatable shields for the first step but nothing practiced actually in the Martian atmosphere yet and parachutes aren't great for heavier things.

You want to use the other two to slow down as much as possible so you're not hauling extra fuel all the way to Mars. Ideally you'd be using ISRU units to generate your return fuel too.