You are wrong. Vitamins are very different. Generally the water soluble vitamins are as efficient and has no problems compared to the natural counterpart.

Where it gets tricky is vitamins a and e. Because it is not a single compound. Vitamin e is 8 different isomers. The synthetic one is only 1 (dl-alpha tocopherol). Which makes you bleed easy.

Vitamin d is best as sunshine, but few if any problems with synthetic d.