In my experience, delivery (volume) is indeed a lot higher on Android, which can be explained by the additional inventory (Play Store Search, Play Store Display, and to some extent google.com search) but also due to the simple fact Android much higher marketshare in many geographies.
As of performance, I'd say "it depends" (which would be a "no" to the question then).
UAC on iOS lacks the premium Play Store inventory to compensate for the poor performance of GDN/admob traffic, but for most developers, conversions & ARPU are much higher on iOS, which helps the machine learning process (more monetization events completion), and more often than not can deliver higher ROAS despite higher CPI. In one particular instance, our Android campaigns did have decent volume but never reached CPA & ROAS goals and had to be shut down, while we could still run iOS profitably, albeit at a much lower spend level.
If we were able to select or exclude networks/placement, the story would likely be entirely different.