Keep the leaderboard separate.
Inactive accounts and smurfs should be removed from the leaderboard.
Everyone should register only one account for the leaderboard and play with other accounts noncompetitive.
There should be an empty leaderboard and a pre-register of 15 games, and only after playing those you can take a place in the leaderboard.
The top 100 can make 9 smurf accounts to block the leaderboard.
L.E. alot of people occupy the 1000-500 places with 1372 points just because they created an account.