that battle system is the centerpiece of the game
Development fatigue is a serious issue, it takes drive to push yourself and work on those parts you hate (e.g) the art if your not a great artist or programming if coding something new. Although I say you still learn from all those failed attempts. Nothing is a waste of time. Its so important to remember where video games came from. Its getting harder by the day with a lot of noise from established games and vanity (we all want to make our dream game). Prototyping is probably the most important part of making a game (besides finishing it) its about getting that spark first, I think with a good prototype you wont have to worry about game fatigue (you tell me).
Not sure if that could help you but I think you're lucky. programming is probably the most challenging part for me,
I think this is chiefly the reason why Lord English can write a battle system as complex so fast... But then again he might be using the pen and paper to write things out as well.