I shoot my vlogs with an iPhone 7 Plus and you can definitely tell where it does well, and where it does not. I shot this vlog during my Christmas break back home with my family, and you can definitely tell that even the iP7+ does extremely well in the sunlight, and not so well in the shadows. One thing I recommend with the iPhones, if possible, record with the front facing camera as much as you can. Yes, the FFC is still good and you can see yourself, but the back camera is far superior in terms of the amount of light that the camera can take in. More light/less noise.As far as editing, I would not use YouTube's stitch software. I'd use something more powerful like Adobe Premiere. Messing with color corrections/filters and other color effects can also reduce the amount of noise in your videos.
If you want to see video quality for reference, the Christmas vlog on my channel was shot with the iP7+