Pity people just go on the raw stats, Khawaja faced some pretty dicey green tracks in his short 6 test career in south africa and against the kiwis and at least fought it out, marsh in current form might not have even survived an over on those same pitches.
The highlighted part being the key. He is in atrocious form, as anyone who has seen him bat in the past (especially early in his test career) would know. Usman, at the time you are referring to, was not. Comparing someone's results when they're batting OK/well, with someone else's results during a big form slump, is hardly comparing apples with apples. You have to compare how they went when they were in a similar boat, like comparing how Usman went in Sth Africa, with how Marsh went in Sth Africa, when they were both going well. (Unless you expect that Usman will never go through a form slump of his own, which would be pretty amazing, considering pretty much everyone who has had a good career for Australia has been through at least one big one at one time or another. I mean it was just a month ago that Mike Hussey (who hadn't played a single test when he was Shaun Marsh's age) looked like he would struggle to last an over in test cricket, making 8 tiny scores in a row, over two series.)
I would say both Marsh and Usman went equally well in Sth Africa, in similarly difficult conditions, with Marsh making our second highest score (44) in the first innings of the Cape Town test, when Watson, Hughes, Ponting, Hussey and Haddin made 26 between them (and faced only 85 balls between them). Marsh helped to hold the fort with Clarke, fighting for 100 balls (against Steyn, Morkel, Philander, Kallis), after we were 1 for 9 and then 3 for 40. (In the match where we then bowled Sth Africa out for 96, before being 9 for 21 in the next innings).
Then Usman did well in the next match, after Marsh went home injured.
That is more a reflection of their overall abilities, as they were both in form at the time and they both did well in difficult conditions (Usman because of the state of the match and Marsh because of the state of the pitch and match).
As for those who don't think Marsh can last as long at the crease as Usman, how about the fact that Marsh faced 623 balls in just 3 of his early test innings (when he wasn't in a form slump), while Usman has faced just 673 in his whole 11 innings career?
If Marsh was making blazing scores, at a run a ball, then you could argue something like that, but the facts are that in those early test innings, he lasted 623 balls for 265 runs and in his last two Shield seasons, when he averaged 59 for each, he had strike rates of 40 odd and about 50. So he has proved in the last three seasons that he is perfectly capable of grinding out scores, while also proving time and again that he can blast top quality attacks in T20 cricket, which shows that he has a similar ability as Mike Hussey, when it comes to being able to adapt to the conditions of a match.
This is why I personally hope he gets his shit together and earns his spot back in the team again in the next couple of years, as there aren't that many floating around that have the ability to bat that way in the different forms of cricket and who have different "gears" like that.
Right now, though, I don't think he should even play in the T20 games for Aust, as he is just that out of form it's not funny (as further evidenced by his poor effort in the Big Bash the other day, compared to his incredible 99 off 52 just a month or so ago in the same comp). He needs to get his form back in domestic cricket, as he obviously ought to have done instead of being picked in these tests, on the back of just one T20 game. This embarrassing stint may just be the making of him.
As for those that are just talking trash and saying Marsh is shit, they are probably the same ones who were saying the same sort of thing about Hilfenhaus, this time last year, saying he would/should never play again, or that were saying similar things about Siddle, in the past year, (or saying that Ponting or Hussey were finished, recently) and just haven't learned anything.