Let me give you an example.

A relative of mine is a drug addict. It started with light pill abuse in his late teen years. Then turned into a serious opioid addiction a few years later. There is wide debate on susceptibility to addiction in terms of things like personality or genetics and so on. Whatever the case his personality certainly seems aggressively directed at being easily prone to substance/drug abuse and to seeking it out. Once he became a full-blown opioid addict, the ability to control his general problem with addiction of course went out the window, it pretty well destroyed his life.

His mother refuses to help him get treatment via for example Suboxone, because she says that's just a crutch that keeps you addicted (equivalent to your reference of replacing one substance with another). Meanwhile, instead, the out of control opioid addiction continues threatening his life. The core of this issue is that not all substances are created equal in their consequences. Suboxone may be a form of crutch, and crutches are often very useful when you have a broken leg.

I've known a few people with opioid addictions, the only ones I've ever seen able to control it had to use treatments like Suboxone. In that case, replacing one substance with another, means regaining control over your life (while you hopefully pursue long-term therapy to permanently kick the addiction) and being able to live mostly normally.

One of those people was a fairly close friend. She had a problem with addictions over many years. Alcohol, cocaine, lighter pain killers, and so on. She was always able to walk back the addictions, until opioids. Once she became an opioid addict, there was no walking that back, it took over every aspect of her life. All of her thinking shifted to short-term obsession to fill the craving. Her entire life became a fireball of destruction: thieving, lying, anything necessary to get the next fix. When you're consumed by that addiction, there is no long-term thinking, there's no next month or next year, there's only sating the drug addiction. When the doctors began cutting off her drug access one after another, she eventually even turned to getting various prescriptions for her dogs. Then buying opioids illegally on the black market. The person you used to know, no longer exists while this is going on, they're an addiction zombie that can hardly be reasoned with (they'll say anything at any time to avoid a discussion or intervention). That whirlwind went on for a year plus, until one day she took Suboxone. I'm sure it's not for everyone, I'm sure it doesn't work for everyone; in this case, it was like a miracle. One day she was an out of control drug addict, a week or two later she was back, normal, able to think long-term again, able to hold a job and reason normally. It was almost as though the prior year had never happened. It's wild to witness that transformation occur in such a short amount of time. So long as she took Suboxone on schedule, she was no longer an out of control opioid addict. She could then pursue a long-term strategy of opioid addiction therapy. Sometimes substituting one substance for another, is about managing addiction in the relative short-term through a better process, so you can work toward the long-term goal of ending the addiction.