IMO Sasori is stronger than Sakura and chiyo. The problem is because Chiyo knows Sasori better,and unfortunately that both Sakura and chiyo are healers. And plus,I think Sasori actually loved his grandmother and thus didn't avoid her last attack,so that's why he lost to them.my problem is that we have a fight like Sasori vs. Chiyo andSakura in which the stronger fighter loses but then the winners don't progress any farther in their skills_ (just an example by the way) It has happened regularly.I just think some of the better fighters should have lasted longer and not kept some of the weaker ones around for as long as they have been. But I guess that is why I am not a manga writer. LOL
I was just like you,but it would be boring if Kishi did that because not all of us are interested in all minor characters. It would be like fillers maybe xd