Personally, I think focus should be on battery life improvement, app management UX, privacy (for example, to this day I can't turn off ALL notifications) etc. I would take 20% thicker iPhone for 20% better battery life and headphone jack any day. Cosmetic changes and thinness-for-thinness sake are worthless.
You would but vast majority of Apple customers would not. There are often calls to "vote with your wallet" and that's what people do. This is why we have no jack and thin phones.
Given that Apple doesn't offer superior phones (with better battery life and headphone jacks), voting with your wallets essentially comes down to getting a Apple one or a non-Apple one.
It is important to note that it is dropping a lot _in China_. Chinese smartphone market is very different from the rest of the world as a smartphone is basically a WeChat machine. Chinese also value novelty and camera capabilities more (by camera capabilities I mean stuff like auto beautification).
Not only in China, though - I'm in Europe, and I see people making the switch in growing numbers - even for the teens, that 2000s "I need to have the newest iPhone" hype has waned and now Samsung & Co. are being considered more.
iPhone omnipresence is pretty much an American phenomeon ... I've seen more iPhones in Vegas in one day than I see in Germany in six months.
According to some stats I have found[1][2] it does not seems like there is any exodus, if anything it seems that iOS gains market share every December (gifts?) and then loses a bit over the year, but the number has been stable since forever.
There are definitely less iPhones in Europe than in US, but that is more of a reflection of the global trend. iPhone was dominant in US because for a long time they had a carrier subsidy system that made it not worth it to buy a phone on a plan for less than $450 (because you paid the same price no matter the price of the phone). Back at that time that's what an iPhone cost.
In Europe the subsidies worked differently so the price was a more important factor.
