For sure cigarettes kills people and based on FDA agenda they should regulates cigarettes but I guess they are not regulating normal cigarettes because it contain pure processed tobacco but it will be regulated by FDA in near future[1]. On the other hand the e-cig is been regulated by FDA because it consider a device which delivers nicotine so can be consider a drug deliver device and besides that e-cig uses a liquid which is not a bio-compound, the liquid is made of chemicals which needs to approved by FDA that how badly it affects the lungs and for that we need pre-clinical research. Additionally e-cig also contains a electrical system so it has to FDA approved to make sure that it won’t catch fire or bust and harm an individual physical. As the need of e-cig increasing day by day(More than 2 million middle and high school students were current users of e-cigarettes in 2016) it should be a class 3 because it potentially consider as a drug delivery device.
[1]https://www.fda.gov/TobaccoProducts/Labeling/ProductsIngredientsComponents/ucm527462.htm