... in a very different competitive environment, and with probably a larger number of failures to get to market (although it would be interesting to put numbers to that, if they can be found).
A senior without android experience is going to have to learn the platform; this will take longer than learning the language. The pace of change updates the best practices often enough to serve as a kind of catch-up mechanic but native mobile does in fact require domain knowledge. I would be comfortable putting a senior iOS dev on native android but certainly not as the lead.