Burgun, K. (2015). Clockwork game design. New York, NY: Focal Press.
Only by finding and focusing on a core mechanism can you further your pursuit of elegance in strategy game design.
Clockwork Game Design is the most functional and directly applicable theory for game design. It details the clockwork game design pattern, which focuses on building around fundamental functionality. You can then use this understanding to prescribe a system for building and refining your rulesets. A game can achieve clarity of purpose by starting with a strong core, then removing elements that conflict with that core while adding elements that support it.