Try it then. As someone who smoked and quit and have had friends who smoked and quit who also had heroin habits, they corroborate the difficulty. It’s a different type of struggle but the struggle is strong just the same.
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.
Here’s one for you https://academic.oup.com/ntr/article/20/9/1038/4096884
But I don't really care. It doesn't sound true but it also doesn't change anything.