according to those who have chronic pain and have used both, heroin is a much more reliable and safer to dose pain management tool than fentanyl. a lot of the dangers come from the illegality like dealers cutting with toxic chemicals to maximize profit and stigma keeping users alone and in the dark away from doctor supervision and advise.
of course it has plenty of abuse, but so does everything. the abuse could be much better managed if it weren't a back alley secret joy and were instead a socially accepted and legal pain medication with education on the risk and standards for purity.
btw everyone should get some narcan, you could save a life some day.