How does Dispensationalism reconcile God's creation is "very good" while its emphasis on human sinful nature being rooted in their free will?

According to dispensationalist theology, sin is not directly caused by Satan - though he plays a significant role in temptation and deception - but rather originates from humanity's free will. However, if Adam and Eve were created with free will and declared "very good" by God (Genesis 1:31), does this imply an inherent flaw in their design that free will itself be a vessel for sin? If so, how does Dispensationalism reconcile God's perfect creation with the capacity for rebellion embedded in it?