About the flat & angular thingy: keep in mind that the structure of rock is quite depended on the forces working on them. In deserts you have quite strong winds which make the rocks more round. Maybe you should take a look at the reference image that were posted here yourself, the rocks you see there are almost all round.
It's true that the structure of rock is very dependent on the forces working with them, so I don't know why you're using cliffs from the Grand Canyon as reference for your cliffs in the middle of the desert - they don't look like the same type of rock, and I doubt they were formed the same way. Not many rivers in the desert, after all.
And yes, you're right that the desert reference previously posted had round rocks, but they're still round in big, chunky forms, whereas yours is round in small forms, giving it the noisy look. The newest one is an improvement, but it still looks too noisy to be tough rock that was shaped by sand blowing around and such. It looks more like a dirt wall to me that's been shaped by water running down it and stuff. Again though, the color could be playing a part in that.
Again, notice that the ground and the cliffs are the same color. And notice how un-detailed the rock walls look compared to yours.
And you can't say it's impossible to make cliffs that share the same color as the ground around them; ptoing and surt did it just fine, and that's the way they look in real life. You'll have to just keep plugging away at it if you want to make it look as good as possible, hahah.
I might try an edit for you tomorrow, because it's something I should be able to draw, too, heheh.