FWIW, I'm on a Nexus running the latest Android O and most of his criticisms mirror my experience. As someone who came from iOS, Android is simply not nearly as polished and I have a lot more frustrations than I used to have. I don't think you can blame it on a cheap Chinese phone.
As an example, in close to a decade of iOS use, I never once had a problem answering my phone or making calls. The phone app (though not the cell coverage) was 100% reliable. I'm currently having an issue where my Android phone can't answer calls. The phone rings, but there's no UI displayed that lets me pickup. It's been reported by many people in forums online and when I've posted here about it, I've had other people say they've experienced the same problem. The only known "solution" is to wipe the phone and start from scratch. It's ridiculous that they can't fix something so basic and essential to being a phone with an OS update, let alone that something like that made it past QA.
I've never heard of the phone app not working. But, it does sound like your issue is isolated. Since you do use a Nexus I would recommend you boot into safe mode and see if the problem persists. It could be a third party app or background service causing issues.
As an example, in close to a decade of iOS use, I never once had a problem answering my phone or making calls. The phone app (though not the cell coverage) was 100% reliable. I'm currently having an issue where my Android phone can't answer calls. The phone rings, but there's no UI displayed that lets me pickup. It's been reported by many people in forums online and when I've posted here about it, I've had other people say they've experienced the same problem. The only known "solution" is to wipe the phone and start from scratch. It's ridiculous that they can't fix something so basic and essential to being a phone with an OS update, let alone that something like that made it past QA.