They are much more predictable, well understood and easier to dose than the chemical cocktail of natural compounds. Please note that I am not saying that there aren’t any useful natural medicines. I am stating that it is better to isolate the active components.
This depends on the kind of herbal tea you use. Not all herbs are as safe as others. Some of them can be toxic if taken regularly (eg. Petasites hybridus, used traditionally in the dorm of tea to treat cold). Some of them also just suppress symptoms. Some of them are understudied and we don’t know whether some of the chemicals they contain are not carcinigenous or something. Medicinal plants are amazing but tricky.