OpenSignal used its own app (available on iOS and Android) to visually represent Android’s fragmentation:

Fragmentation is both a strength and weakness of the Android ecosystem. When comparisons are made between Android and iOS the issue of different API levels, and the vastly different devices running them, is often emphasised. In this report we examine the extent of Android fragmentation and analyse its impact on both users and developers.

Even though the report is specific to OpenSignal, it gives a good representation of the disparity among Android devices. The number of different versions and screen sizes out in the wild must give headaches to app developers.

Google’s strategy worked. The company has a wide range of devices into consumers’ hands to whom they can show ads to. This is to the detriment of app developers, who have to put in so much work. iOS, on the other hand, makes it so easy to build an app that it makes more sense to go ‘iOS first’.