The burden belongs to the one who wants to prove issur. There are countless tshuvos from countless poskim over the last 300 years paskening heter re: smoking. Cigarettes have gotten safer over that period of time. Also, knowledge that smoking causes lung cancer (in the form of medical studies) has been around since the forties and fifties. Reb Moshe knew about medical studies.
It’s one thing if y’all were so into making heterim because the previous generations made a mistake as proven by current scientific studies. But y’all aren’t (myself included). Be consistent.
As to the op, no, it isn’t. It is unhealthy, but does not reach a likelihood of life-threatening harm to the individual smoker. Shomer pesoim hashem. There are rabbis that disagree with the above. Ask your Rabbi for halachic guidance pertaining to yourself, if you are unsure.