I think the app boom is in decline, but I really don't see how illustrating lower growth for the 20 most well known apps demonstrates this. Less people downloading Facebook, WhatsApp, or Instagram? Account for how many people already have it! There could be a saturation of those very well-known apps.
There's a lot more to consider once you look at how the entire app market is changing, rather than just the very top.
There's a lot more to consider once you look at how the entire app market is changing, rather than just the very top.