Not GP but I can strongly relate to it. Most of the programming I do is related to me making a game.

I follow WET principles (write everything twice at least) because the abstraction penalty is huge, both in terms of performance and design, a bad abstraction causes all subsequent content to be made much slower. Which I can't afford as a small developer.

Same with most other "clean code" principles. My codebase is ~70K LoC right now, and I can keep most of it in my head. I used to try to make more functional, more isolated and encapsulated code, but it was hard to work with and most importantly, hard to modify. I replaced most of it with global variables, shit works so much better.

I do use partial classes pretty heavily though - helps LLMs not go batshit insane from context overload whenever they try to read "the entire file".

Models sometimes try to institute these clean code practices but it almost always just makes things worse.