Regarding the initial question: the Mythras system turned out to be everything I wanted in a D&D game when I was in high school: a customizable series of magic systems intentionally mean to create a diverse series of different (and thematically focused) magical traditions, an armor system that applies well to more use cases than 16th century Europe, and a levelless, flat-HP system that makes experienced characters vulnerable to ambushes or superior numbers (and therefore means that experienced archmages are less durable than soldiers out of basic training, which makes a certain sense, but wasn't reflected in D&D). That same system, in which combatants have both active and passive defenses, also allows for Link or Conan to show up, in the sense that there are use cases wherein a skilled fighter can survive front-line combat, provided they avoid the above pitfalls.

So the system didn't so much open my eyes to new possibilities such as it opened my eyes to the fact that there were better ways of seeking what I had sought in RPGs for some time.