Proof: The Lord Ruler was upset that he wasn’t the one who was heralded as the hero of ages, so he named his children the Heralds so they could herald him.
Theory: The real reason that Wyndle doesn’t want to be summoned as a Shardblade is that his cousin was once bonded to an Edgedancer, but when he was summoned as a sword, his radiant dropped him and he cut/fell his way to the center of the planet and was forever traumatized by the experience.