Yeah it's all very straightforward when you look at usage patterns. Often meth abusers will smoke multiple points across a day (a point = 100mg). As a result they stay awake for days straight, don't eat, and often will engage in enormously risky sexual behavior (this is the dirty secret of AIDS btw...it arose in the context of the "party and play" gay subculture where people would smoke meth or other drugs and have sex for hours and hours and hours straight with many, many different partners...but I digress)

The infamous "meth mouth"? That's caused by not sleeping and by just overall letting one's life go to shit. Amphetamines do suppress saliva production, so they aren't great for teeth, but it's 95% the lack of sleep and other associated behavior patterns.

I've taken pharmaceutical adderall (which is 75% d-amp and 25% l-amp btw), and pharmaceutical dextroamphetamine (100% d-amp), and illicit, presumably cartel-sourced, and presumably very pure d-methamphetamine. When taken orally, d-meth is, in my opinion, simply a superior ADHD drug (it is much more dopaminergic than amphetamine, yet causes less peripheral stimulation, so you get a much more favorable ratio of positive cognitive effects to negative peripheral effects).

However, the moment someone starts taking (especially smoking, since the RoA of any drug makes a massive difference in addiction, doubly so for meth) hundreds of milligrams, it becomes a completely different drug. It becomes super deleterious to health through the sleep deprivation and risky behaviors alone. Furthermore meth has a unique property that amphetamine apparently doesn't, which is that it can become directly neurotoxic in large doses (meth has some serotonin release, like a much, much weaker form of MDMA, whereas amphetamine has virtually none, so it's possible that that's the mechanism). This is why in the research literature there's a lot about methamphetamine "neurotoxicity", but the papers conveniently omit that if taking oral doses comparable to what's given for ADHD, it's not neurotoxic whatsoever (and frankly may be neuroprotective, especially against traumatic brain injury).

So yeah, your analogy to Adderall is spot on. I've often seen people derisively refer to Adderall or other amphetamines by saying "we're basically giving kids meth!". Which is true in a sense, except it's really the other way around: meth is really not very different from Adderall. If someone were to smoke 100mg+ of amphetamine, their body would break down the same way it does in a meth user, except possibly for the direct neurotoxicity effect I mentioned.