Sorry, I'm a little confused. Where exactly is the "chrome>google>images>wallpaper>save image>gallery>set as" sequence you're talking about?
If I were to download a wallpaper from the web using mobile Chrome, I'd bring up the page with the full-sized wallpaper, then long-press the image and select Save Image. This will download the image to the Downloads folder. Once it's there, you should be able to select that image as a wallpaper, and it should be full resolution. Sorry if I'm totally misunderstanding something!
EDIT: Never mind, I realized that the sequence you're referring to means that you're opening Chrome, then going to Google to do an Image search for wallpapers. Rather than going to Gallery for the Set As option, what happens if you go to your Wallpaper Picker? Does that give you options to select images from your various folders?