Ask anyone who has tried both. Ask all of the people who tried smoking in their teens and didn't continue.

I had a minor headache for a couple days, and that's about it other than cravings. I have yet to meet anyone whose quit who had significant withdrawal symptoms, and some of them have smoked for decades.

Comparing a clinical doses of opoids is not the same at all as street heroin where no one is controlling the dose. Your doctor will keep your dose standardized, when you do heroin you will eventually get bags that are way stronger, your tolerance will increase to a level that a doctor wouldn't prescribe to someone unless they were on hospice. Once you have that tolerance, quitting is incredibly excruciating, you will be sicker than you ever have been in your life. Maybe after a week you will stop being sick, and if your lucky after 2 weeks the extreme depression might ease a bit.

It's just not a good comparison. Ubiquitous access vs extremely difficult access is the only reason people compare them. The substances themselves are not even in the same ballpark in terms of physical addictiveness.