The only reason they mentioned him was to show us readers how badass Sasori is, thus, his existence is only a fuel for Sasori's awesomeness.
That's a good point.

Chiyo also said that the kazekage puppet was Sasori's favorite and most powerful. But, it doesn't have to be the most powerful puppet simply because the 3rd was the strongest sand ninja ever. It is just appropriate having the strongest puppet be made out of a Kazekage as opposed to something ordinary and generic like a salamander or scorpion. It doesn't have to retain of the 3rd's justsus or strength in order to be the most powerful.

That fact that the puppet is made from the body of the 3rd Kazekage is really meant to be symbolic of the strength of both Sasori and of the puppet. It adds some shock effect to the story.