When I hear 'mainstream phone', in my mind I picture an iPhone or a Samsung. So yeah, Linux phones are definitely not achieving that this decade. Though personally I don't think they necessarily need to, at all.

Point 4 is probably not happening any time soon, if ever, either. Rest is slowly being done and progressing, so I'm not seeing any major problems there.

I don't think anyone realistically expects a Linux phone to compete with an iPhone in terms of ease of use, quality of life features or UI/UX. As far as I've seen, people just want a decent phone with basic functionalities like long battery life, good camera, easy to use and smooth UI, maps and navigation. All while being more private and secure, of course.