First of all, we code native everything in C/C++ to guarantee a the smallest possible footprint of code. We heavily and dynamically use ASTC compression for textures, reducing file size further. We estimate our games will be at about 10% in file size in compared to other similar games.
We try to generate as much content as possible in a procedural manner, reducing some of the need for files with hefty size. Obviously, authoring is required to create addictive and fun to play games. Games should be hard and fun to play, not hard to understand!