Sasori stomps hard, he's like Gaara v9001.0 and actually worthwhile for fighting someone like Kimimaro. His attacks are precise and will hit him, Kimimaro won't be able to stop the poison, bones or not. He will get paralyzed, and his bone defense is far from automatic like Gaara's sand. Sasori's attacks were making gigantic craters from destroying the ground, Kimi just can't compare to the level of hax.
I'd say restrict poison to make it more fair, but yeah.