How would you quantify league parity??

I've been exploring the ebbs and flows of parity within various sports leagues primarily to justify betting heavy favorites. If a top 5% team plays a bottom 5% team what can we expect to happen? I would like to hear any ideas on what metrics would be used to measure and quantify the overall level of parity/ "competition abundance" within any given sports leagues. I'm pretty open to any ideas so any suggestions, references, or resources for ideas are appreciated.