Well, increasing prices every year is not sustainable in the long run - at least if you want sales in the triple-digit millions every year - but neither is the Android hardware ecosystem that relies on Apple for ideas for new phone-designs and people buying new mobile-phones basically every year.
None of the Asian handset-makers has a service-business like Apple. They have to pay Google (and MSFT) for the Android-Google-Apps. What do you think are they making money on?
Maybe they'll siphon-off all your data - but that isn't really sustainable either.
Apple assumes, you're using the device for five or six years. Else they'd never have backported iOS12 to the 5S.
Once the Chinese have sold a cheap phone to every Indian, what are they going to make money on?
It's not that people in Android-land are spending all the saved money on Apps and accessories.
Are you really going to throw-away (resale value is terrible) a perfectly working (sort-of) OnePlus phone just to get a newer Android-version?
OK, they use cheaper flash with less underprovisioning , so you'll get random crashes after a year or eighteen months and you will cave in and upgrade sooner than you want - but how often are going to do that circle-dance before you start to question who got the good end of the deal?
I admit, my current phone is a 4S (really planing to upgrade real soon now) and quality of Apple-devices has gone down since then, too. I don't know. But for now, I'm convinced I'll not get any more value from a phone than from Apple. Four-digit prices or not.
If I get a phone with an A12, I certainly won't upgrade before it stops being supported by iOS-upgrades - and probably wait a year longer.