Sorry but disagree.
The UI / UX can make or break an application, and is also a key reason why many of us choose one editor over another. If Apple applies their UI language (the current photos application) to Pixelmator, I will have zero interest in using it.
There are many other apps that use Core Image, Metal, their own, and many other fundamental Apple APIs that I have zero interest in using. it is how they build their pretty client over these core APIs that makes it a joy to use.
We all can get weather information in pure text, with ASCII graphics, get weather the way NWS presents it, or something better like how Dark Sky, Carrot, and other applications present and produce information to us.