It's not about what people or scientists say. It's the wrong frame to think about it in.

Pharmaceuticals these days run as businesses, and its not financially beneficial for them to even quantify the medicinal qualities of chemically unprocessed plants. Because you can't build a competitive advantage around something like that. So, while they often take inspiration taken from plant based compounds, usually the essential compounds are extracted, a synthetic process developed to manufacture them, and only the medical properties of the resultant product studied via trials.

It would do well for publicly funded medicine to reserve some funding for quantifying the medicinal properties of plants used directly.