It doesn’t make sense to me to sort Pokemon by CP in gyms. CP doesn’t really mean squat for battles, so why are the organized that way? Dragonite, Snorlax, Rhydon, Gyarados & Vaporeon are consistently top defenders, because of their high CP.
Organizing by level could prevent this and would allow high level Pokemon to also be able to be in a gym, regardless of max CP.
This could also add a variety of defenders into gyms like Chansey, Ditto, Blastoise, Venuasaur, Charizard, Slowbro, Poliwrath, Nidoking & Queen, Omastar, Victrebell and Vileplume that don’t typically make it into gyms or are bottom defenders.
I also think a prestige bonus who be a nice incentive to diversify gyms. 10% prestige bonus for adding a grass type, 15% prestige bonus for 6 Pokemon with different types, 25% prestige bonus for having 10 different Pokemon in a gym. This would make it easier to prestige, harder to take down, increase types of Pokemon and reduce gym stagnation.
The exact opposite could also happen, -10% prestige for having 3 of the same pokemon in a gym, -15% prestige for having the same top 3 Pokemon, -25% for having 5+ of the same Pokemon in a gym.