Yes, i kind of disagree here. Mainly on why android is popular. See, android became popular when the only smart phones in the market where the expensive iPhone and the Windows Mobile devices which were aimed mainly towards enterprise. Android won many new users because it was cheep and so markets who cant afford iPhones jumped to Android and some stayed with the old nokia phones. At that time, users didnt have much choice and they couldn't refuse android for its UI, but now in these years where UI and UX are a huge focus for many companies, users are starting to care about UI and how comfortable it is to use. Why do u think google jumped to material design and is trying to unify their UI design guidelines if the UI wasnt important as you claim?
WP didnt get marketshare because of 3rd party devs not building apps for the platform and because the massive hate wave it received from reviewers, carriers and other people in the market who influence users choices. If you ask the 3% of people who use WP, i am sure one of their reasons on why they chose WP would be the UI and its uniqueness.
I will give u an example, if u had 2 software each from a different company and both do the exact same thing in the same efficiency. But one have a messy UI that is a bit confusing and the other has a beautifully designed UI, comfortable and clean. Would u go for the ugly or the nice and clean UI?