Sometimes the last place person is actually in first as soon as they complete their comp/items. I have been on both ends of this.
One instance, I was trying to build a yordle comp. I didn't get to complete my Yordle comp until I was in last place with 20 points. As soon as the comp was completed though, I randomly beat both of the top 2 and never lost again.
In another instance, I was dominating first place all game.... Then I went against the last place person who just completed their Yordle comp. They decimated me and no one beat them again. This is the person I learned the Yordle comp from. Yordles comp is strong but takes forever to complete.