Although technically correct, imitation is a deceptive term. Vanillin is the key flavoring agent found in vanilla. Synthesizing vanillin is not creating an imitation, it is synthesizing the exact same compound that exists in nature.

There is literally no point in growing vanilla to extract vanillin if vanillin can be synthesized artificially for much cheaper. Though if you're going for compounds other than vanillin that exist within the vanilla plant itself... that's a different story.

Rule of thumb in these cases is to use natural vanilla for items that do not get baked. Such as ice creams or cake frosting. And use the artificial vanilla for baked goods. And even then I lean towards the natural stuff when I bake. Real vanilla has a complexity and depth to it, like a fine cigar, you can sit and savor it.