That's been done before though, ie telltales batman. At least for me, it wasn't surprising at all that they made Thomas a dick.The only modern origin story for batman is Batman Begins, in which Thomas Wayne is presentd as a man for the people and Batman trying to save the "innocents" of Gothem from the criminals.
What Joker does is take that idea and flip it. Thomas Wayne is not a nice guy, and the "innocents" are what created one of Gotham's most menacing criminal figures.All of which culminates in the Origin of Batman.