Well, I wasn't speaking for everyone nor did I mention the iPhone. The fact that many other OEMs use Sony sensors doesn't automatically mean the photo quality will be good as the image processing is usually the deciding factor. And I don't recall the Z line ever being considered the best smartphone camera. I also said I'm going to reserve judgement until we can see some real world reviews because you may be absolutely right. The fact that the smartphones cameras that are currently considered to be the industry best--the Galaxy S6 line, the Note 5, the G4, and the iPhone 6+ all have OIS does not fill me with confidence is all I'm saying.
First, the comparison to a 60" television using the same resolution is irrelevant in most regards--TVs don't run on batteries and the PPI is a fraction of what it is on a 5.5" screen.
People may want 4K resolution on the video but the benefits are realized when they watch on a 4K monitor or TV, not on their phone. We cannot see the difference between that 4K video if played natively or at 2K on a 5.5" display. Nobodies complaining that their phone display resolution just isn't high enough at 2K but you know what they are complaining about? Poor battery life. So instead of improving that, let's throw an even bigger draining feature into the phone to solve a problem nobody is bitching about. That's why I say it's simply stupid.
And I'm not saying we should never have 4K resolutions on phones, just that there is so little reason to do so now, especially considering the diminishing returns and associated costs of having it (primarily power).