10 minutes build time for the Spotify app - I don't do mobile development - is that a long time? I've only briefly touched a point of sale iOS app and compiling took maybe 30 seconds.
A lot of the Spotify app isn't perhaps visible at a first glance. Besides the key features I'm sure you're already familiar with, there is also an extensive number of 3rd party integrations (cars, wearables, voice, social sharing etc).
The app as a whole is 1-2M LOC Objective-C & Swift.
I feel this is another Dropbox moment [1] on Hacker News where the hyper-smart ones here dismiss a whole technology/company on their most simplistic assumptions about what the product actually is doing.