Is suffering a proof against intelligent design?

An atheist has argued with me that suffering is going against "intelligent design" in humans and animals. He would agree that pain is vital for our nature to indicate when something is wrong, but he is saying that people are experience deep suffering which can change someone entire life and some people can never recover (like huge depression, mental illness etc.) Also there are unnecessary suffering like, why suffer when someone dies? He said that if God is perfect in creation we shouldn't have this experiences... I was defending in two ways: 1. original sin 2. unknown reason God may have to allow this, since he is all knowing, we cannot argue that we are imperfect, because we do not see the entire picture and we cannot understand fully what is the purpose we were made for... Therefore our current features could actually be perfect for a specific purpose. I'm wandering how would you answer this question; Is suffering a flaw in intelligent design?