I don't know why you'd assume you're the outlier. Never mind the differences between physical and psychological dependence and problem use (which can happen without dependence, and one can be dependent but not using problematically), you personally experienced underwhelming withdrawal effects on multiple drugs that don't all affect the same parts of your brain, and some more physically addictive than others (benzos on top of that list). As for your friends, you know about their struggles because they had struggles in the first place. Just as the news doesn't report things when nothing bad happens, it's unlikely that, with the potential of stigmatization and jailtime, most people would volunteer something that caused them no issues but can only cause issues if they let it be known. If I were in your shoes I'd not assume that you and this guy happens to be the outliers, but rather, selection bias, the well-documented history of our drug laws being based on racial panics (Chinese for opiates, cocaine for African-Americans, marijuana for Mexicans, the crack sentencing disparity, et cetera) that happens to fund a lot of the economy via the prison-industrial complex, it's not much of a leap to think that a great deal of the harm linked to drug use is linked really to the various behavior undertaken to hide from detection and not necessarily from the drugs themselves, most of which - diamorphine included - are classified as having some medical use somewhere, although for whatever reason MDMA and marijuana are classified as having none. I think it's not hard to buy into the idea that problematic use is not the outlier because that's been taught to us for decades. But if your personal experience doesn't indicate that, why jump directly to thinking that you're the odd man out?