Of course, because addiction is one distinct measurable thing - not multiple things like physical addiction, psychological addiction, which substance builds up a higher tolerance the quickest, which has the worst withdrawal symptoms, etc. etc. It is a very different thing between which drug is easiest to get hooked on and which is easiest to get off of once you use it heavily. What about the potential for relapse once you get off of it?
I guess in your world meth is a 4.5556 addiction level and heroin is a 6.33314. Case closed.