Why do my photos on LG G6 seem overly compressed?

I've just come back from a nice hiking trip where I took lots of photos that looked good on the LG G6 screen.

But looking at them closely, there is very little detail - they've been heavily smoothed.

Here are those rocks in the midground:

I have the image quality settings at 4:3 (13MP) and this particular image is 4.4MB (original here).

Is this normal? Is there anything I can do about it?

(I'm using Google Photos, but the screenshots and original image above come from exporting directly out of Gallery, to email.)