Heroin addiction is 90% looking for or doing something to get more. It’s an incredible time sink. It’s impossible to have a meaningful life like that.
What medically administered heroin does is allow people to get that time back so they can rebuild their lives. Once they see that things are better, they become more successful when finally coming off of it. Even if it takes forever, they are still productive members or society instead of a drain.
Like 'skellera says in the sibling comment, heroin is an incredible time-sink. The methadone programme I am on (provided free by the UK NHS) is something that will let me gradually reduce the amount of heroin I'm taking, and eventually yes, get clean. After a couple on months in, I'm down to ~25% of what I was taking daily before, and that should reduce further to zero over time.
A methadone maintenance program will gradually increase the amount of methadone prescribed, while the user reduces the amount of heroin they take, until the user is 'stable' and no longer using heroin. After that I certainly would like to then stop taking methadone too, but in some cases the maintenance can continue indefinitely and it would still be considered a net positive outcome...
What medically administered heroin does is allow people to get that time back so they can rebuild their lives. Once they see that things are better, they become more successful when finally coming off of it. Even if it takes forever, they are still productive members or society instead of a drain.