They simply used the whole herb. Perhaps they dried some of them, but I seriously doubt they soaked them in water, prior to cooking. There would have been no need to do so in those days, and soaking in water would make the herbs last less long.
Steeped teas will be "less worse" (as regards toxin-creation via heat) than some cooked foods, such as cooked animal foods and foods not cooked completely in moisture, but that's all. That said, if one has a particular health-problem and finds some herbal teas useful for that, by all means try it. I doubt herbal teas are good for anything but temporarily resolving certain symptoms, though.
