Modelling the basics of a human lung isn't all that difficult. You can see the effects of vaping on an enclosed space just by having the smoke pulled into an enclosed space like they used to do for cigarettes. That would give you substances created though the vaping process and likely to stick in the lungs. Longer term effects are drastically harder obviously as it doesn't take into account the cleaning mechanisms in the lungs but for basic verification that something is toxic that's not a difficult bridge to cross.

Now when you get into whole body or things with mutations such as cancer I agree with you while heartedly. While we can understand in a petri dish how to kill something in a human you've got to worry about things like delivery, hidden single cells, toxicity, and drug proliferation all of which can be different in every single person with a cancer. In biotech we're still just barely out of the dark ages.

To bring this to the original topic, we're still in the dark ages with fields like economics. While we understand many of levers that exist we have little idea of how and when to effectively pull them.