Hrm. It isn't clear enough to me how exactly this system is going to evaluate and rank character's power, so i'll just throw in what i had in mind and see if it matches with your ideas.
All charcters have individual powers and pieces of equipment that they use in combat, don't they? Regeneration, fire control, sonic blasts, wings, swords, armor and ect.. My idea was to rank all the seperate abilities of a character, the sum of all their ranks being the characters tier.
Example: Dave has four powers and a single piece of equipment. 2 powers score rank 7 out of 10, another 2 - 4/10 - and the equipment scores 10/10. Sum that up and we get a tier 32 character, who can find a fair match in the 27-37 tier range. A seperate multiplier may also be added to modify these numbers according to these abilities' combined output: for example, Dave scores 8/10 in this category, and according to this result, his tier number is adjusted to 80% of its initial value - 25.6, 26 rounded.