OTOH, a lot of those markets coming on stream might have a lot of "zero-rated" providers - Google makes a lot of money from ads when people search on the open internet. Less so when most of their activity is restricted to a few apps because consumers don't have to pay for the data use.

Most of the people who are accessing the web for the first time are from poor countries like India and Indonesia, so the effect on Google's revenue is much smaller than the number of people would suggest. Other drivers of Google's growth are just as important: (1) People who are already connected to the internet are getting richer and are spending more time online; (2) Google continues to improve its algorithm matching advertisers to users

This. Google (and Facebook) can generate more revenue by leveraging the accumulated users personal information in more invasive ways, irritating their end users. They can sacrifice long term growth for short term gain (or not). I think some of this short term growth slowing is due to that - pulling back from the most egregious practices because of scrutiny.