So the new talking to excuse the iPhones cameras lack of some pureview features is to make the shortest possible time between shots and the launch time of the camera app the most important characteristic of a phone camera? Seriously, if this all you care about , just get an iPhone and quit whining. It takes 2 seconds to launch Nokia camera on the 1520 and 1 second to switch to the smart cam interface if needed. If 1 second or so really makes a difference, well then so be it, it is a niche scenario in practice. It takes about 2 seconds max if you are shooting dual capture on the 1520 which should be same for the Icon as it is the same camera with the same SoC, a difference of one second max is hardly a deal breaker for real people but the reviewers still have to whine about something. If you want more flexibility, the Nokia camera interface is likely faster than any other camera app on the market as you have easy acess to all the most important settings.
Also, if we want to discuss the focus speed and catching moving things, well, unless you really need to catch a picture of something in 2 seconds, which you likely do not all the time in the real world, the Nokia camera app allows you the ability to set the focus mode to manual. In many cases, just set it to infinity if the object is not to near you, and you then got the ability to snap a picture instantly even in low light when you pull the shutter which is faster than any other camera phone on the market which still has to focus before snapping the picture.
If we are getting into details, the Lumia phones are also much faster for me for taking quick pictures as I happen to live in a colder country where you usually need to wear gloves of some kind for the better part of the year. If I want a picture, I just push the manual camera button to launch the phone while picking it up from the pocket and then I can quickly take pictures with the camera button without removing the gloves. If use a regular smartphone, I have to first remove the gloves before even thinking of taking pictures. Hence I would miss all those all important pictures which apparently need the fastest possible time to start taking pictures.