So the real problem in the rules is the words "weeks in a row". As you describe it, if you use an addictive substance, you must make an addiction test. The formula just tells you when, and lets you know if there is a chance that occasional use keeps the threshold low.
So Kamikaze has a rating of 9, which means that one use of Kamikaze triggers an addiction test in two weeks. If you only use it the one time, that gives you a week to drop the threshold from 3 to 2, which, depending on your meta (trolls and orks would be better and resisting this due to bonus body) you could get addicted after one dose.
So focus addiction has the potential to bring on an addiction test immediately? If you have 5 level 3 bound foci, and use them all at once, your addiction rating is 15.
It looks like hermetic mages have the best odds of avoiding focus addiction.
