The problem with a parachute, even a very large one, is that the atmosphere is so thin that you are still going at hundreds of miles an hour when you hit the ground. That is just too much of a hard landing for most spacecraft to survive though specially hardened penetrators can.

If the parachute is big enough, you can have a conventional landing just as for Earth. Simply use aeroshell, and then parachute, and parachute down and the parachute will slow you down enough so you get a soft landing.

The problem is deploying those parachutes and making sure they work. You can work it out with computer models, test tiny parachutes etc. But at some poitn you have teo test it with real parachutes. The parachutes on Mars so far were tested by firing rockets in suborbital trajectories and then releasing parachutes and required many tests.

To make even larger supersonic parachutes will require many expensive rocket tests. NASA are working on this with their Low-Density Supersonic Decelerator - Wikipedia

NASA "Flying Saucer" Supersonic Parachute Fails Test [Video]

I don’t think their plan is to use a parachute all the way down. Rather it is to land larger masses, of up to 5 tons so would probably still need a complex landing system.

This is just a rough idea of how it works. For more on ways of landing on Mars with supersonic retropropulsion or large supersonic parachutes etc, hear Robert Manning talk about it here Mon, 03/28/2016 - 14:00

For more details about the complex landing sequence on Mars see my answer to Did the landing sequence of the Mars lander Schiaparelli really have to be so complex?

which I’ve also written up as an article for my Science20 blog here: Why Do Spacecraft Like ESA's Schiaperelli Crash On Mars So Easily?