But, since only a minority of people get addicted to heroin (i.e. the evils of heroin are overstated), and since no one is actually seriously arguing that viewing TikTok is as risky (23-38% chance after exposure) as trying heroin, or has as bad side effects, I think it reveals that comparisons to heroin use in arguments against TikTok are hyperbolic and disconnected from reality, by empirical data.
I don't think that follows from your premises. Who is overstating the evils of heroin? Plenty of people argue that viewing TikTok (or AI-optimized short-form feeds) has bad side effects, mostly in the direction of eroding your ability to pay attention to anything less stimulating.
One thing that makes heroin more benign is that it's "finished" in some sense. The drug trade will find more addictive substances (e.g. fentanyl), but a vial of pure heroin isn't going to gradually become more addictive over time in ways that are imperceptible to the user but visible on the backend because the loss function trends downward.