Of course it's relative. I'm comparing. Being relative is both implicit and synonymous with comparing rates of harm between two things. But you simply can't definitively say something is damn near harmless relative to cigarettes when you don't actually know what harm it causes, and nothing you've said changes that we don't know what harm it causes. Available evidence strongly points towards not being nearly as harmful, but that's at a relatively short term time scale.

I also don't see how comparing vaping to not vaping is a bad faith argument. If smoking causes lung cancer at 13 to 23 times the rate as not smoking, it would seem important to compare vaping's rate to both of these, along with any other health effects. It's one (albeit imperfect) baseline. Sometimes, as in the case of living in a polluted city, the baseline varies and should be controlled for in studies. You yourself emphasized relative harm. So comparing harm of doing something to that of not doing it is exactly what you would want in order to get that relative relationship.

More on pollution-- maybe living with air pollution is worse than vaping, but then living that way and vaping would be worse still. Again, there's that relative harm again. These studies have been done with traditional cigarettes, showing living in pollution increased lung disease but smoking then increases it even more, again all relative (in most studies) to "never smokers". An important piece of research to find out for vaping as well.

Finally you put a straw man up against my arguments when you talk about banning hypocrisy: I don't advocate banning it, and you're right that it seems a silly conversation to talk about banning vaping if you're not thinking about the same for cigarettes. For my part, I generally want vaping to be treated on par with cigarettes, excepting I think it should be marketed as a quitting method, not an alternate life-long choice.