Why don't apple just have an options menu to let you choose between 4k @ 30fps and 1080p@60fps?
All other smartphones offer this choice so why not apple?
I have a Note 3 and playing back 4k and 1080p videos on my PC (1080p monitor) shows a clear improvement in quality in the 4k videos
What is your screen's resolution? If it's higher than 1080p, then that's why there is an improvement, though I doubt your screen is a 4K screen, so you aren't seeing the whole improvement. And I think that's the point. The amount of improvement you get wasn't deemed necessary for the current market. The number of people who would get anything out of 4k video are so limited that Apple decided to work on other features.
I am personally way more bummed at the choppy performance of the 6 plus than it's lack of 4k video. If I was the guy that keeps his phones for 3+ years (around the time I think investing in a 4k tv and monitor might actually be worth it) I would probably care more. I'll have this device for, at most, two years, so it's honestly a moot point for me (and I am guesing many, if not most, others).