I think you offer some very valuable observations. If a person follows a good diet and lifestyle, gets a bit of exercise, elmininates stress and toxins from their body and environment, etc., then there may be little need to supplement other than to make sure no vital nutrition is missing - and given our mineral depleted soils and processed foods, that is a very valid concern,
Yoga is wonderful for exercise, proper body alignment and functions and stress removal.
However, some conditions that are serious and perhaps ones that have built up for years may need more the natural healing power of herbs to help restore the body to where good practices can keep it in good health. I don't think herbs are here on good mother earth just for us to look at.