Lore Based Power Ladder
Even though all the champions in game have around the same level of power (loosely, at least) in the lore some champions are obviously stronger. Here's what I imagine the power ladder to be.
TIER 1 (GODLY BEINGS - 
- Only two champions are near worthy of this tier, the forger of stars and the embodiment of death itself.
TIER 2 (ASPECTS) -
- While they have human bodies, they embody extremely powerful entities.
TIER 3 (DARKIN) -
- While only one is in the game, Darkin are extremely powerful creatures. Aatrox could easily defeat most champions in battle.
TIER 4 (ASCENDED) -
- While not as powerful as they may appear, they still are nothing to scoff at.
TIER 5 (GREATER MAGES) -
- These are not just the normal mages that inhabit Runeterra, these are mages that are all so powerful that they have to potential to take over the world (and many try to.)
TIER 6 (GREATER WARRIORS AND BEASTS) -
- Few humans can reach this level of power. Through either finesse, brute strength, or both, they can destroy nearly anything.
TIER 7 (LEADERS) -
- These champions aren't the most combat proficient, but they have massive political power.
TIER 8 (LESSER MAGES, WARRIORS AND BEASTS) - ALL UNLISTED CHAMPIONS - These are all the other mages, warriors, and etc. Strong fighters, but nothing too special.
TIER 9 (FRIENDLY SPIRITS) -
- These champions just do not have very much power, they are not built to fight.
TIER ? (UNKNOWN POWER) -
- The lore of these champions are both very vague. While they are both definitely powerful, their true power is unknown.
If you think any champions should be higher or lower on the ladder, please let me know. I would love to start a discussion.