Don't metal stitches used for breast reduction hurt more than dissolvable stitches?

Metal sutures are also called skin staples and yes they do hurt more, are awkward to remove, and do leave track marks on the skin. Almost all surgeons in the US probably use dissolving subcuticular sutures which are completely under the skin and don't need to be removed and will not track or mark the skin. If your surgeon is talking about skin staples, you might consider a second opinion.

From what you're describing it sounds as though whoever had the breast reduction surgery had staples placed for skin closure.  This is not typical for this type of surgery.  Typically, dissolvable sutures are placed under the skin to obviate the need for suture removal and to also try to improve the cosmetic result of the incision and potential resulting scar. In my practice, I have never used staples for skin closure for breast reduction surgery.  I have always placed the stitches under the skin which dissolve which make it much more manageable and easy for the patient.