You have removed all incentives for playing the Expert game at Champion level except for the small number of players able to compete with the previous top scores.
The changes could have been better communicated to players, not everybody reads the forum or Buzz (not sure if it was on the latter.) It would have been helpful (and still would be) if something could be put on the main pages for Who's the Expert. I was puzzled by what was going on and I am likely not the only one, I finally was enlightened (but disappointed) when I came here and saw this discussion.
Actually, there is still an important incentive to play at champ level after winning - you can help your team's league rank by getting a good score in your best topic every day!
However, if you are looking for some stats that encourage personal improvement, we could consider adding a personal high score, similar to how the original ELO had your own number beneath the list. And unlike with ELO, you won't have to worry about your less favorite topics dragging down your rank, so now you can shoot for a lucky win on all those topics you may have avoided because those bottom half finishes were poison to ELO ranks. So, while there may be less incentive to replay the topics you won as champ, you have even more reason to try those you still lack the champ victory for!