Of course degree matters. Healthy and Unhealthy are not binary categories.

Both alcohol and meth are harmful to health, but the degree makes one manageable and the other not.

Obviously? Dosage makes the poison.

Yes, it matters because the government has an interest in improving the public health. When you reduce access to vaping that decreases the number of vapers and increases the number of smokers. So the relative risks of each are important in deciding how much you want to promote/restrict access to vaping.

If vaping is just as bad as cigarettes than you probably want to make vaping really expensive and hard to get. If it's completely risk free you'd want to subsidize vaping and make sure it's available at every store. The best evidence looks like it's 5%-10% as deadly as smoking which means we probably don't want to restrict it too much.