It could yield a significant number of additional iPhone purchases. Especially since one of the use cases for Android was “not having to use an App Store”. If the iPhone has that, then many that are buying Samsung devices because they’re the most Apple Android devices can just buy the Apple device.
If in 5 years, Apple’s device share grows by 20% or more, putting MORE of the EU’s citizens on the iPhone and, thus, driving additional profits to Apple (while simultaneously not bringing any new hardware/software vendors to the market), then success? Though, I don’t expect the regulators had in mind “we need more folks buying iPhones!”