I mean still, you gotta have robots handling fuel on an alien world and you still gotta land the rocket on something other than some random patch of dirt. Yeah, you can engineer things this way and that, make the rocket land on just about anything solid, reduce the fuel you land, make robots that are more reliable or expendable. Anyway you look at it the engineering challenges are massive. No matter what you're going to try, it affects Earth much more than than the way Tang and freeze-dried ice-cream did.
On what pad are you going to land the rocket? You've got to at least level the ground and clear it of debris before a landing. That's gonna take some big construction equipment, even in 0.4G, likely not with a human anywhere near. Likely, you'll need to pour something akin to concrete for the pad, which is not an easy job for a suited up human without any real rad protection. Robots are going to be a major part of any Mars mission as Mars is not a great place to be outside and doing skilled labor.
The carbon and oxygen needed can be extracted from the atmosphere; the rocket only needs to bring the hydrogen - just 1/12th of required fuel mass.