That's not true. "The science isn’t fully decided" means that long-terms effects are extremely hard to measure, it literally takes decades. The amount of liquids of different flavors is so big that you can't realistically test them all. Different flavors require different chemicals, you can get the same taste with different chemicals too. Yes, basic liquid is probably less harmful than cigarettes, but even for that there's not enough data to say that this is a scientific fact.