It's about sensor size, not MP...
Big sensor with less MP is always better than small sensor with a lot of MP.
Phil.
As an experienced photographer of nearly 50 years both with film and digital , I can tell you this is true up to a point.. The rendering engine in any digital camera makes all the difference. You can have a high end lens and larger sensor but if the rendering engine isn't up to par the images can be fair to poor..
Now combine a good lens, sensor, and rendering engine and you have a good camera capable of high end imaging.
My personal tests comparing the iPhone 5S and Galaxy S5 tells be the Galaxy has the overall edge..
The Galaxy even beat the fool out of the iPhone in high ISO shooting with much less noise than the iPhone. In fact high ISO with the iPhone shows it to be a very poor shooter in that respect. Average shooting in well lit shots to Galaxy showed cleaner sharper detail in both highlight areas and the mid to low zones..
As another poster has pointed out MP don't really matter.. An 8MP camera is every bit as capable as a 16MP camera. It's what I posted above that really matters..