There are more apps on the play store than the iOS store, and apks have always been easy to work with and had this same advantage.
If this advantage has always been present, why aren't the apps already better than iOS apps?
And it seems to be a compelling package - pretty much every app beta I care about has switched to it (even those that already had an existing off-Play-Store setup).
Many businesses started on iOS first, producing an Android version as an afterthought by contractors. Others produced a minimum viable product which made them money, so they felt no need to iterate. This means upstart competitors can easily take away the market share of established products. It's a good thing for startups.
Most successful startups began with a niche. Look at AirBNB's cheap conference attendees or Microsoft's Altair owners.