This is just a minor suggestion but add a third title, and run it akin to a division system based on rankings.
Players can move up or down a division based on how well they do in their respective division.
There's the world title, the middle title, and the lower title. What if the world title could be held indefinitely, but the middle and lower title can be held for a maximum time? What if they could defend the title a maximum of 5-8 times, and if they reach the max, they'll move up the rankings into the next division. When this happens, the lowest ranked member of that upper division is moved down to the lower division.
This allows everyone to at least compete for something, even lower ranked members. They have opportunities to challenge and move up the better they do, and members who get taken to a lower division have the opportunity to compete for a title immediately!
Expanding on this too btw, one way to do the divisional system would be to have head-to-head to move up and down the rankings.
Example: You have 12 people predicting weekly.
#1 is the World Champion
#2 is the challenger
#3 & #4 compete to become the next challenger
#5 is the midcard champion
#6 is the midcard challenger
#7 & #8 compete to become the next midcard challenger
#9 is the lower champion
#10 is the challenger
#11 & #12 compete to become the next lower challenger.
If #2 loses the title match, he's bumped down to #3, and the winner of 3/4 is bumped up to #2.
If #5 defends long enough, they vacate the title and move up to #4, while the former #4 is moved down to #7-8