Making your game general

ITT we discuss how to collaboratively design our games.

>> closed system centered on game engines

Huh? I'm writing my own game engine, not using some closed source game engine someone else made.

Gamedev revolves around creating stuff within a game engine or modifying the game engine, thus development proceeds within the closed system.

What's that supposed to mean? Are you saying I shouldn't make a project because software development is more general?

The scope of software development in a game project is limited to game engine or its libraries functionality required for the game and nothing else(except maybe multiplayer servers, but it doesn't sound like your 2d hobby project will reach that stage).

Why not? What I'm doing demonstrate knowledge of GUI stuff, debugging, making a decent-sized project, file IO, exception handling, OOP, etc. Sure, it's not the most amazing project ever. But it's a start. You don't start off by writing really advanced shit.

Games are actually very advanced shit as a concept, they're a complex closed system, their own little world. Like a modern browser provides a closed set of interfaces, a modern game engine is providing a virtual world interface - a virtual machine for game scripts/maps/media. 2D hobby projects will be a limited set of the above and your ideas of growing skills inside this closed system will be limited by demands of game engine(not much for a simple engine).

But I'm making the game engine myself, and that's a bulk of the work for it. I'm not spending a ton of time on the stuff after that.

See? you are making mostly the engine and all you will program will revolve around the engine, its limitations and interfaces within it. Its mostly throwaway code that will never be reused.

The only way to get better at programming is to program more. I am doing this as a project to program more.

There are programmers who "program more of the same" and there are programmers who "program different things", guess which one gains a better set of skills?
If you spend all time around one project, your skills will adapt to that. Dedicating your time to "one true game engine" will not expand your horizons or gain you new skills, it will be slow refinement of what you need.