I think several things contribute to the apparent lack of detail in this shot.
1) The lighting. The sun is iluminating the subject head-on and at a low angle, causing the image to be flat. But, on your crop, take a look at the branch of the tree which is half in shadow. There's actually quite a lot of detail there!
2) This is a wide angle shot. The scene as a whole looks fine. Look at the detail of the fine branches in the tree and the flower bed off to the right. Of course, if you crop in, you'll see less detail. Take the same shot at a longer focal length and see what happens.
3) Well, the lens. I've had a look back through some of my shots with this lens and I'd say they're about the same, although I don't often shoot down at f11.
I think you just need to play a bit more. Try manually focusing. Try different apertures. You'll find it's actually quite capable.
Here's a similar low angle lighting shot, but the sun is oblique to the subject allowing detail in the brickwork to show nicely.