I think this is one of those situations where you count dollars rather than heads.
My understanding is that the "next billion users" push that all the big companies are doing is a bit like putting macs in schools. It is a long-term plan 'cause yes, the developing world is poor right now. maybe those people who are poor now won't be poor in the future, and if they know how to use your ecosystem, that's great for you. It certainly seems like a good idea, but I don't think it's where you make your money today.
I really think if you were serious about that plan, you'd come out with a giant low-end phone; You remember the thinkpad W series? something like that. big and clunky and cheap. Apple needs an iphone 5c level cheap plastic reskin of last year's big phone for that.
The market you're really talking about them capturing with a small premium phone is "rich people who have multiple devices and want a small phone and when they can't get one they buy an Android phone or make do with an SE". I'd wager that's small in most terms, certainly in Apple terms -- whether you're talking dollars or heads.
But what do the top-end Chinese consumers do when Apple doesn't have a phone that appeals to them? They buy one of the other flagships that run WeChat, and Apple loses them. That's big in Apple terms, missed-expectations-warning big.
In the olden days, when Apple was much smaller, they were ironically freer to just make the best device possible because success would be meaningful in very small markets. The OG iPod saved them despite selling relatively tiny numbers. Nowadays, markets that used to matter significantly to Apple -- education, media, creatives -- are allowed to wither and die because they are a blip on the bottom line.
I don't see what could change that, though. They now prioritise growth/financials/share price over pure products in a very calculating way, but what corporation doesn't? You need an exceptional mandate to do otherwise, and only the Bezos's and Jobs's of the world get those.
So the pity is that as a result we'll continue to see Apple pushing hard into services and (probably) media, because that's where it can smell growth. That might keep the numbers up, but I suspect it's going to transform what Apple is even further away from the "make great products" company we knew into ... something else. (Probably something less great, given their track record with services, tbh.)