Hi @perrichan 
Lets see what we can see here.
A great place to start.
The first thing that I noticed when google image searching the photograph you provided was pretty low resolution imagery overall. But the best photo that I found was one that had a lot more cropped into the photo than the reference that you provided.
From what we can view here the proportions of the original, the practice, and the google image photo are all different when we regard their frames. If you want to copy something to understand its essence whether it be a photographer's photo or a renaissance master we should use the same size frame that the master did. We have to do this because we are backwards engineering the mysteries of an individuals thought/creative process and their intention. Was it a painting for a lords hall? A phone wallpaper? A bookcover layout for font? As the student that frame matching makes it easier for us to find what we missed in the study to make the necessary changes to our work.
Although your copy is more warm in the light and cooler in the dark the one thing you have missed is the depth of space that the original provides by moving some branches and having more view of the hilltop in the background as something to look at as we wander through the piece. You've blocked us into the foreground and middle ground and we feel trapped.
Your original and your copy in thumbnail form, how you should often be checking your work when painting.
And a quick paintover in thumbnail form.
Spot the basic shape differences and the warm and cool relationship differences with this new perspective?
First thing, hide all the brushes you didn't make and start with the lasso tool and an airbrush simple round. You can do a study in 5 minutes. Or a layout sketch in 5 minutes. Your brush can be made to be hard or soft edged with hotkeys, shapes like leaves and branches can be made with the lasso tool.
Look at this work by Mike Azevedo the art director at MAR.studio
There are few if any custom brushes in there its all a flat marker style brush with no texture, lasso tool and an airbrush for edges. The focus of the painting is the house if he were to flesh out the painting for a splash image or a spread then the piece as a whole would be more fleshed out.
To reach your goal, take even more detail out. If you had an hour to do this alla prima outside you wouldn't have time to render flowers, you would be focused on the shape and color of the flowers that they make as a group. And you'd be having to mix paint constantly and fast. Or blended with the shadow shape the tree is making the way I did in the paint over.
To achieve your goal of simplicity Limit yourself to one brush, or two brushes. (It takes a while to find versatile brushes or make them and learn their limitations) And set a timer. Start with 5 Minutes. Do four five minute studies. Then do three ten minute studies. Then do two fifteen minute studies. And finally one thirty minute study. What do you learn? What do you see as important? What ways do you solve the problem?
I did this paint over to illustrate my points with one brush. I liked your flowers more than what I did btw, they were just fine they served their purpose, but for the lesson of simplicity I did that paint over.
Out of sheer practice I see the compositional shapes are off in your copy and the temperature is wrong, the frame proportions were wrong to start. Do I worry about the amount of flowers, and how good they look, or the amount of pixels representing sky are coming through the leaves? No! Not until i get the overall composition. Get down the relationships of the right shapes and colors and overlapping elements then finally move on to one or two spots of detail. That is if we want to make a painting, not a photograph.
But if you want to speed paint concept art, just know artists make brushes they need in the moment for specific paintings then never use them again. I don't know how many tutorials and presentations I've seen where the instructor is using two brushes and not all that crazy set they put out. People just don't edit their brushes down, but like to have a large arsenal of brushes if its needed.
Besides when you are studying you move to a better scene with your alla prima group, or change the google earth photo....ya know? To study is to repeat. With repetition comes simplicity. And with simplicity comes speed. The more you do the less importance you will places on pieces that you have made because you are studying what it is that makes you happy and what makes you an artist.
Lastly to be fair to yourself, the reference image you chose doesn't really have a focus point. It looks like it was designed to be a layout for font on a book cover that has a generic scene in it. Its also fuzzy which doesn't provide you the artist with enough information as to what the light is doing in detail on spots where you want the viewer to focus.
I hope that gives you some perspective on where you lost what made the picture beautiful and what the photograph was possibly meant for. Find some great landscape paintings or photographs that have a focus to them. You did a great job and maybe got a little lost but that's okay. Start big and finish small.
Cheers
