Too much grain in my photos

My phone: iPhone 7 plus with latest iOS 10.3.3. Purchased few weeks ago.

I searched about grained photo issue in iPhone and found out there is a manufacturing defect. Also I tried using different apps apart from the stock camera app. Because I saw that in many articles mentioned that camera app use some kind of algorithm to reduce noice and it cause some water color effect which is true I can see water color effect when zoom my photos.

I'm telling this because I compared unfiltered photos I took from different phones. I even compared a photo I took from my old Sony Ericsson K800i which had a 3.2 mega pixel camera. Photo I took from K800i is better than iPhone one. Colors are not that good but edges were sharp and clear.

Then I used an app called VSCO and took some photos. It gave me better quality images than stock camera app but still I saw too much grain.

I'm not comparing photos with a DSLR quality camera (I'm not that stupid 😀). I'm comparing photos with other high-end phones. And I want to educate community whether it's a good option to buy iPhone if someone's main focus is for photography or to take high quality pictures like Apple advertise on their videos and events. We all know that functionality wise there is no smart phone that can beat iPhone.

So please help me to figure out what is the actual problem here. Below I'm going to post photos I took to compare.

iPhone buit in camera:

Photo took from VSCO:

Samsung Galaxy S8 Photo: (I had to reduce image size because it was larger than 2MB)