The RATE of obtaining geodes is the same for each geode, DURING THE RIGHT CONDITIONS. But those right conditions are NOT the same for each geode. Snow Geodes can be gotten in areas with 95% blizzards over the year, while Flame Geodes aren't even hitting 5%. So the rate isn't the issue, it's the conditions for that rate to occur.
What about changing the weather in Ru'Aun Gardens so it is affected by killing elementals? Kill fire elementals to increase the chance for fire weather to occur the next day, up to 12.5%. You could even have NM elementals/avatars spawn during those maxed weather conditions, which drop geodes or avatarites!
Weather science for fun and profit!