no system is perfect. besides, if you want to have a full tier system that always determines winners, the simplest solution is to implement a complete tabletop system. But everyone here knows that this isn't a stat-based RP.

In here, a tier system that covers all general levels (and not just best-of-best) would be a rough idea. A skilled (or lucky) weakling can still kill one of the best given the right situation. For example, even the most powerful mage tends to leak out in all the wrong ways if someone sinks a blade or arrow into their heart or brain or somesuch. Or for a more martial example, a man (or woman) dressed in a perfect suit of full plate mail—which is the medieval equivalent of a tank (as someone here coined it)—will still die they get an arrow through the eyeslot of their helmet or simply get thrown into a river or lake deep enough not to stand on the bottom of while keeping head above surface.