Like others have said, it is a bit of a budget lens. Nothing against that, but knowing it weaknesses can help you get better shots (like knowing when to stop down more, or when to zoom in lens but take a few steps forward if possible, etc…). Shot at f 5.6 you say. It’s not wide open - I’m guessing - but it is close to it. Maybe closing down a bit more and raising ISO would’ve been a better compromise. But that’s hard to tell after the shot is taken, this is what ‘learning your gear’ is all about :). Maybe you don’t like the noise at higher ISO’s, and you rather have a softer look from your lens, maybe not. I can’t make that decision for you.
There is (was?) a rule of thumb that if you shot something at 55mm, you should not go slower with your shutter speed than 1/55th. But if you have lens or sensor stabilizing, you could go slower. But if the wind is blowing, leaves are moving and you’ll get motion blur from that. And that rule comes from a time when we weren’t pixel peeping images. So I take some margin in my mind always. In other words, your 1/160 sounds fine to me. Depends if there was really strong wind :).
Also, although not always fun if you are a ‘walking and brining my camera with me’ kind of shooter, but a tripod always helps more with shots like this than people imagine when they are just starting out 
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Also, make sure lens correction is applied, specially for Darktable. It can help with ‘chromatic aberrations’, minute color misalignment in the lens, specially at distant edges it can help clean things up some times.
Also, Darktable doesn’t really apply sharpening by default (at least mine doesn’t out of the box 
). And a bit of sharpening is always welcome, but do not overdo it.
Programs like Adobe Lightroom / Adobe Camera Raw always apply a bit of sharpening, even when the sharpening slider is at 0% so to speak. It’s in their camera handling for specific sensors.
Also, if you have an image that looks pretty good when viewing at 100% in Darktable, exporting it and resizing it down for the web can take away that sharp feeling. That’s normal, that is why sometimes an ‘output sharpening’ step is done → sharpen after resizing down, depending on expected viewing distance / method. (If you’re really picky out these things, you apply different sharpening after sizing if it’s for the web, for a small print, or a big print, or even different kind of printing methods, etc…).
And then I want to exit with saying that sharpness and contrast go hand in hand. If you have more difference between blacks and whites, they stand out more. If things stand out more, you see them as sharper / more detailed. Sometimes lowering the blacks or raising the whites (global contrast increase / local contrast increase) and do quite a bit for your perceived sharpness of a shot.
So, TL;DR: There are tricks to get more out of your shot, and a bit of careful processing is always needed. This is not that different to the first shots I have taken by simply ‘aiming the camera and clicking’ with the kit lens that came on it. Slowly you learn a few things that you need to keep reminding yourself about, things that can make a simple shot better. Or mistakes you learned from. And slowly they become automatic in your mind .
