Sure, Vader was a bad guy in the OT. I mean, obviously! But there are important moral differences at play. Not every bad act is morally equivalent. For example, being part of, and supporting, a genocidal regime is not necessarily the same as committing genocide oneself. (Just as aiding and abetting a violent crime can be distinguished from the violent crime itself.) Sure it’s bad, but not as bad. When it comes to the destruction of Alderaan, Tarkin was the far worse actor.
I agree with twoyennan though and I wish we got a more earnestly heroic Anakin in the PT. We only kind of get a facade of that in Episode 3. If Anakin and Luke’s stories are meant to complement one another, having Anakin become a mass murderer in Episode 2 feels like a total misstep.