One of the cornerstones of the Mars Direct approach is that it takes advantage of the solar system's orbital mechanics such that the actual trip is relatively s

One of the cornerstones of the Mars Direct approach is that it takes advantage of the solar system's orbital mechanics such that the actual trip is relatively short in comparison with the duration humans have spent in space so far. I think you probably have a point about 40 tons aerobraking in the atmosphere and then popping a parachute, but I wouldn't expect either to be a deal breaker. The NASA Design Reference mission is essentially a modified version of Mars Direct, so I would expect reading up on this would provide solutions to these problems, or at least it will go into more detail than this brief article.