A true tummy tuck tightens the muscle from the pubis to the xiphoid and removes skin in a manner that is appropriately tight and aesthetic. Most general surgeons do not wish to take on the additional risks of this procedure when repairing an umbilical hernia. Plastic surgeons are trained in aesthetics.
The incision needs to be properly placed, the umbilicus needs to be contoured to make it attractive and the skin needs to be removed in a manner that tightens the skin without excessive tension. I would get a second opinion from a plastic surgeon.