What is a "whole game engine"? Ideally an exported game only includes the parts that are actually used and those should be much smaller than 50 MB for a simple example or even for most games.
The official “export templates” that you use need to be able to run any game you create with the stock engine, so they are fully featured. You have the option (and it’s recommended) to compile your own export templates, at which point you can specify which parts of the engine your specific game does and does not need (e.g. turn off the 3D, turn off the more advanced UI components, etc…)
