It took a while to realise there was a way of getting the full resolution images from what looked like low-res uploads.
There are two obvious differences: the A8 has chosen a darker exposure, and it has used much heavier noise reduction. Both of those are software things, so in principle may improvide with updates. The question is however whether Samsung are likely to actually address this: it's a budget phone (so won't get the effort allocated to it that a flagship would), and Samsung have often shown a belief that people hate noise so much that they'll accept any loss of detail rather than see a hint of noise (i.e. they have chosen to do this). So I don't know whether they will fix it.
However, I don't think this is a fault in your phone (though obviously a diagnosis based on one image should not be taken too seriously!). This looks to me like a processing choice they have made. I would check the camera app's settings to see whether there is anything you can do to improve quality, such as reduce the amount of compression - I've never met a phone camera which lets you control the degree of noise reduction, but lower compression might still help.
