500k is supposedly 5% of the itunes store. That's 10 million apps, madness! There must be hundreds of thousands with approx 30 installs...
This blog post is a bit old but shows around 1.25mm apps on the iOS App Store at the beginning of 2015.
http://blog.appfigures.com/app-stores-growth-accelerates-in-...
I also think 500k apps is either a heavily padded number or has an extra 0... I doubt one company accounts for more than 33% of apps.