They had to have the propulsion gear and fuel, so that part was going to be there anyway.
The part that was NOT necessary was the cab;e to lower it, all the motors and gear to lower it, and the extra fuel to hover and then accelerate away. They should have just landed.
When spaceflight costs are calculates in hundreds of thousands per pound, that was unnecessarily complex.
I am NOT saying it was not a great accomplishment, given the complexity - it was a great success. But, the costs for that success were higher than they needed to be because of the complexity.
The previous landing was a masterpiece of simplicity- they inflated balloons and bounced to a landing. I am not sure I agree with that one either, but the payload was light enough to be worth it.
Just look at how Elon Musk landed two huge and heavy boosters. NASA would never have been able to accomplish that. It was too simple and common sense, for a government program.
The cable system also kept the rover and its instruments further below the landing rockets and their thrust, so the rover didn’t start its mission in a massive debris storm.
Around 3:55 in this animation with interviews:
https://www.space.com/16889-mars-rover-curiosity-sky-crane-landing.html