[Xperia Z3 General] One Twelve:
No. The problem is you think 20.7MP will allow you to pixel peep and see more detail. I don't think that is possible nor is it the intent. Diffraction will affect sharpness around 13MP. So what purpose are more pixels ? its to help with interpolation when downsizing.

Technically if they are viewing it on a full HD screen a 2MP is all that is required. They arent' going to be zooming, they are consuming. A 20mp downsized to 2MP will look better than a 13MP downsized as there is more data to play with. As will a nokia 1020 41MP downsized to 2MP.

Now we're getting into a different area. if you have a low rez camera, the focus on what you want in the picture come in. if you have a 4mp camera or a 8mp camera you will have to think a little bit more about your shot so as to not require to crop in as much later. You will have to crop the edges in any case as corner to corner sharpness on a 25-30mm is iffy with even the best glass.

As for zooming, optical zoom solves this problem. But you don't have that, well more pixels will help you to a point but not beyond. so maybe consider a phone with optical zoom.

Let me give you another example. Say you want to take a portrait. Now portraits aren't taken with 30mm lenses, they are done with 75mm upto 135mm. How to do that with a fixed focus lens like on your note 3 or z3. You stand back further. At this point you have two choices. you can use digital zoom to frame or you can zoom out and then crop later.

To turn your 25-30mm lens into a portrait lens you will throw out two thirds of your image to get the perspective right. So you are left with 3MP-6MP equivalent image. Downsize it and you have 2MP nice and sharp and devoid of noise. Decent enough for sharing.

Its funny how people say smartphone cameras are replacing compacts ? no, you can't compete with optical zoom and never will. if you opt for fixed focus lens you are compromising. Deal with it.

You did not post the 20MP downsized to 2MP.

Don't use camera HDR you are better off bracketing and doing it manually. Course you will need a tripod.

Try stiching, again tripod with nodal point and you can make massive panaoramas.

Get a phone with optical zoom or wait until sony makes one. Or since you live in Germany check out the panasonic Cm1 with its 1 inch sensor. Its not a good idea to go with v1 of any product mind.

Otherwise what people are doing here is exactly what you're supposed to do.

What use is any photo ? if not to make it nice to look at. That is where YOU come in and the camera becomes a mere tool. This is the bit i find rather difficult. Thinking how i will arrange things in the frame, what to show, what not to. How to convey what i want.

They've been saying this since the Z1. You ever look at the file sizes of Z3 compared to Z1 for 20MP, lot larger right. With Z1 they said too much compression. Also auto on Z1 would bump ISO up a lot so manual got much better photos. Too many people complained so with Z2 auto got a lot better. Since file sizes has increased since Z2 i don't think you will see much improvement with further updates. marginal at best. So go learn about photography. your photos will improve by leaps and bounds.

G2 does not do low light it takes HDR same with G3.

the iphone 6 runs ios8 which has manual controls opened up, ask your brother to try 3rd party apps from the appstore, the stock iphone 6 camera is crippled. All he has to do is use a slower exposure with low ISO and manage to hold the camera steady. Should get quite close to Z3.

Know what ? even iphone5 devices will get ios8. The gap with low light will close much more with manual controls.