You are right. But you are using a rational brain.
Whether an up or a down is the interest of a tweaker, not an addict. An addict suffering withdrawal from pain killers which he can no longer acquire is going to get relief the quickest, easiest and cheapest way possible. Meth fills that bill. That the relief is contra-indicated, doesn’t last all that long and causes an even more painful crash means nothing. He will just get and use more. The euphoria is the only goal. Once meth became difficult to manufacture, heroin comes to fill the void.
No, Meth doesn’t fill the bill.
Heroin and Meth are two entirety different drugs and Meth does nothing for opiate W/D’s except likely make them worse.