w/r to the f2.2 lens. There really isn't going to be all that much difference between F2.2, F2.0 and F1.8. It's about 1/3rd of a stop difference. The difference in light collection is negligable, the difference is depth of field is also negligable. An f2.2 lens is also likely to be smaller, lighter, sharper than an F1.8 lens. It's really not something to get caught up about.
Regardless, without knowing the size of the sensor, the iPhone 6S f2.2 lens may capture more light than the competitions f2.0 and f1.8 lenses anyway. I'd be interested to know what the T-stop of these lenses is relative to their marketed F rating.