They do it that way because 90% of all pictures taken by a smartphone are going to be viewed on a smartphone.
It's really just use cases and preferences. I prefer the Samsung processing because at that screen size those issues vanish.
Agreed... horses for courses. Most people like the "Samsung" look for obvious reasons, but I often use my phone photos for other projects (and often crop, which is guaranteed to amplify problems). I like the idea of a Pixel because it'll let me perhaps leave my proper photo gear at home more often, although I'm still considering an S7 because it can also shoot RAW.
Having a wide aperture is not a hindrance when it comes to focusing. Matter of fact, all cameras autofocus with the aperture wide open (this allows the camera to use more light to focus), it's only when it comes time to capture that the aperture is stopped down to the metered value.
One thing a wider aperture does require, however, is more accurate AF, although I'm not sure how much different the DoF is in practice for f/1.7 vs 2.0 on such a tiny sensor.