Why would the rate of harm parents cause their children be equal when parents have all the power over their children?
Again, it all depends on what you mean by "harm", what you mean by "children" and what you mean by "power". Estranged adult children do enormous emotional harm to their parents, by the fact of the estrangement itself, and by some of the abusive behaviours subsequently perpetrated by the children. Example: getting their parents to repeatedly apologise to them by text and then screenshotting the apologies and posting them on social media for the purpose of entertainment and humiliation - regrettably a common sight on Reddit. These actions are justified by slogans such as "We didn't ask to be born, therefore we don't owe our parents anything" which are common currency on estranged children's forums. By any definition, this is emotional abuse.
Discussion about emotional abuse almost always focuses on actions by the parents, hardly ever on actions by the children. I'm simply trying to redress the balance.