I feel like I shouldn't have to try heroin to understand this. A solid paper on the topic would suffice.

No it wouldn’t unless you can consistently reproduce any found results among differing populations and I have serious doubts such a paper, with said follow ups, exists.

OK, then I'm going to go with "doesn't sound true"...

There needs to be a term for this mindset where people won't entertain a thought or idea unless there's a study proving that thought is correct in all cases. I can guarantee the person you responded to is a weightlifter.

That's not the case here at all. I believe lots of things without studies. Something like "heroin and cigarettes are equally addictive" doesn't sound right to me - that's why I need evidence to the contrary. It's a somewhat extraordinary claim, therefor I require some evidence.

A simple Google search returns hundreds if not thousands of results.

Here’s one for you https://academic.oup.com/ntr/article/20/9/1038/4096884

That paper does not look like it actually measures addiction, and I don't want to sort through hundreds or thousands of results...

But I don't really care. It doesn't sound true but it also doesn't change anything.

I've quit both cigarettes and a middling amphetamines addiction.

Quitting cigarettes was trivial. I decided not to buy a pack that day and then never bought another pack. That's my anecdotal contribution to the discussion.

Less anecdotally:

Opioid withdrawal, in extreme cases, has killed people from persistent vomiting and diarrhea. It has measurable physical symptoms with an understood pathophysiology largely connected to the cAMP-signaling system.

Nicotine withdrawal is far less understood, to the degree it has been classified at all (mostly in studies of mice). It certainly has never killed anyone, you're not going to shit yourself to death. They're not comparable to one another.