The phrase "than one's last one" is an idiomatic expression that means "more than one's last performance or effort." It implies that a person has done better than they did in their previous attempt or has surpassed their own expectations.
Sentences with «than one's last one»
While this year is much better than last year, it's still HOT. (remcooks.com)
As for effort, well... I enjoyed the tank years more than this last season. (sbnation.com)
But agreeing a lot more than last season when he had me scratching my head. (sbnation.com)