Value is personal. For me, the iPhone Camera might be like a 25% if I can leave my DSLR at home. A $300 phone isn't going to approach the quality of an iPhone XS, so I'd have to bring my camera.Yes, Apple's support is superior.
Yes, iOS and Android is a differentiating factor and if you are into Samsung/Android stuff, Note 9 might be somewhat more appealing.
Well, I wrote 90% for $200 and I think that is reasonable. 90% of the stuff people do on there phone is calling/messaging, media consumption (some videos, music), social media, browsing the internet and casual taking pictures. A phone for $200 will easily do that.
The +5% for $300 will get some casual gaming and slight boost in all of the above.
For $500 you get +4% like mobile payment features (Apple Pay and clones), better quality of camera (probably dual camera), wireless charging and maybe water resistance.
And everything above that is niche features such as good AR, awesome screen, awesome camera etc.
Simply having a web browser, camera, and gaming doesn't mean anything. If the browser is a pain to use, they aren't on equal playing fields. If the phone is sluggish, glitchy, and constantly force closes apps, that's not a level playing field.
Support, software, services are worth way more than 5% to me. Maybe 25%. Camera maybe 25%. The A11/A12 chips help with every task, maybe worth 20%. Add it up and the $300 phone might be 30% of the phone I wanted. At that point, the phone is not something I want to use.