I think it's true that tea companies tend to use lower-quality white teas for blending and flavoring to produce flavored white teas. However, it's not true as a general rule that flavored teas are inferior in quality or flavor to pure white teas. Some companies are better at blending than others, and some do a good job of producing flavored white teas.
I also think that there's a difference between blends that involve whole ingredients such as herbs, spices, or dried fruit, or that involve traditional scenting such as with flowers like Jasmine, Rose, or Osmanthus, and teas that just use scenting with an essential oil (or worse, artificial flavoring). I strongly prefer the teas that have been traditionally scented or blended with whole ingredients.
I also want to point out that lower-grade does not necessarily equal lower quality or inferior flavor. Personally, as a general rule, I tend to like silver needle tea less than white peony tea, which I tend to like less than shou mei, my favorite style of white tea. Yet shou mei is the lowest grade of the three, and silver needle the highest.
It's largely a matter of personal taste.
So, if I were advising someone, I'd say that it's good to be a little skeptical of flavored and scented teas, and to do some research into them, but if you can find a company that sells traditionally-scented teas or that uses ones blended with whole ingredients, you're probably going to be in good shape. (And honestly, some people do like tea scented with essential oils or even artificial flavors, I know it sounds sacrilegious to the purists but it's really a matter of personal taste.)