Take a look at Lord Zaeon in Zanarkand. His statue thingy looks just like all of the other Fayth Yuna prays to. Except his soul is gone from it. This is because Yunalesca summoned him to defeat Sin, then Yu-Yevon grabbed hold of him, and finally he was defeated by the next high summoner's final aeon. After Yuna & Co. do this to every one of the aeons she has summoned, all of the fayth statues she prayed to are empty, just as Lord Zaeon's was.