As much as I agree with you, the main problem is this. Others versions of fun, by no means all but still a great portion, involve an Unviable Mercy is a Mercy with no Rez. People do not like to see their kills reversed, their hard work undone by the (not so) Simple press of a button. As long as Mercy is able to undo kills, she will not be ”Fun” to anyone but those who play her.
Also, the whole “Cult” thing, it is much much easier to illegitimise someone’s views by demonising them, making them seem bad. To get the people to rally behind you against the great ”Evil” that has befallen the land.