I dare to contradict.
The opposite is true. Even in difficult light conditions the results are fascinating. Never judge image quality by YouTube videos; although they're supporting 1080p60 since some weeks, they will compress the original file. I saw the "waterpaintings".
Have a look at the original file (p.e. wirelessly via iPhone/Apple TV HDMI, supports 60p) on a modern LCD TV. Clear, brilliant images without almost any digital artifacts! Very little jitter and less moiré and rolling shutter (on very fast moving objects or cameras) ever. The 60p are more important than 4K believe me (ask any video gamer). The image stabilization is top-notch as well (
both iPhone 6 and iPhone 6 Plus).
Here I've put some examples (okay it's YouTube but you'll get an idea) in my blog:
Tests der iPhone-6-Videokamera
There are slow-mo shots and shots taken while riding bicycles and trains.