How is natural vanillin any better than synthetic vanillin? Matter is matter. Organic molecules are identical whether a plant produced them or a chemist.
Not the parent, but that's a good example : I cook with vanilla sticks sometimes, and it's just 100x more flavorful: I can leave the vanilla stick "marinate" overnight in my preparation and the flavor will be much different than pouring vanilla extract (real or synthetic). Synthetic vanilla sticks simply do not exist, and I think the impurities and other things in those vanilla sticks contribute to the taste.
Vanilin itself is a good example of the exact same molecules, but for instance I remember on chemistry class discussing banana flavor extract: it tastes "like banana" but it's not actually the same chemical component. Making a cake with that chemical and labeling it banana bread could be done and probably won't taste the same.
How is natural vanillin any better than synthetic vanillin? Matter is matter. Organic molecules are identical whether a plant produced them or a chemist.