A Base leaderboard is where all players rank against each other for a given matchday based on the sum of all their base points scored in a given matchday.
Pookyball boosters play no role in Base Leaderboards. All Pookyballs play on equal terms. Yes that means that Legendary or Commons is basically the same.
10% of the prize-pool rewards are distributed in Base Leaderboards.
Pookyballs are also distributed to winners.