Nettles have serotonin, histamine, and acetylcholine. Serotonin could benefit certain mood disorders, and acetylcholine supplementation can reduce certain kinds of headaches.
As with all natural foods/medicines, I think you'd typically see only minor benefits over long-term supplementation. Much less powerful than modern medicine, but perhaps fewer side effects when taken properly.
You're right to be skeptical though, lots of snake-oil salesmen in the natural food space making dubious claims. Blueberries are probably much healthier for you than eating Cheetos, but probably not that different from other berries. I appreciate scientists studying which species have the most nutrition, but variance in freshness and growing conditions are probably the biggest factors in nutritional density. ex. fresh raspberry are probably better than old poorly grown blueberries.