First I wanted pointed few things about Columbus of all things:
Columbious wasn't trying to discover Amarica or prove that the earth was round. In fact, Columbious believed the earth was flat, and continued to believe it until the day he died.
I'm quite sure this is not true. Whole Columbus expedition was based on assumption Earth is round - but smaller and there is no Americas.
Columbus was in fact believing land he discovered was Easternmost part of India, and he died believing that. (I mean if he believed world is flat why would he he sail to India - straight West).
Amarica had already been discoverd by other exploers, most notably the Vikings and Ferdanad Majelien. Columbia's was actually trying to find a faster Trade Rout to Asia. Instead, he wound up in South Amarica.
We can say America was discovered by multiple tribes before, but when we say discovered in Columbus context we speak about perspective of let's say Eurasian civilisation. Viking settlements were earlier - but they were not known to Europe as whole.
Ferdinand Magellan was 12 when Columbus reached Carribean Islands. His discoveries - are decades later than Columbus.
-Third. When Columbis finally did land, he and his crew were greeted peacefully by the natives, who Columbis and his men began to kill and enslave, until very few of them remained. He then took, along with the slaves, all the Spices, Fabrics and Gold his ship would hold, and returned to the queen and his homeland in Victory.
That is vast oversimplification of longer process than truly in fact lead to downfall of Taino culture of Carribean Islands. (Not to absolve Spanish of their crimes, but it's simply not like Columbus came with his three ships and killed 2 million natives on multiple islands and then returned victoriously). Also reactions of various Taino tribes towards Spanish differed - there were violent reactions.
Bonus Fact: Two of Columbiouses ship, the Nina and the Pinta, are Sailor Slang for Prostituets. Being a God Fearing man, Columbious made them name the third ship the Santa Maria.
This is not really certain.
Primo, by custom all Spanish ship or almost all had Saint's name and unofficial surnames.
We know Nina (girl) was names Sainta Clara. And that her nickname was rather pun on her owner Juan Niño surname.
Santa Maria was nicknamed "La Gallega".
Secundo, neither of those ships were Columbus property. They all had owners - mentioned Juan Nino, Cristobal Quintero (Pinta), Juan de la Cosa
(Santa Maria). So it seems not improbable they all have their names estabilished before Columbus organised his expedition.
Now in terms of Luccio's words, I see no reason to treat it as Holocaust denying - I mean considering overall stories of DF I could make guess about sligthly right-wingish libertarian believes of Butcher - maybe, but how such interpretation would even hold in overall scheme. Especially consdiering Butters character?
But I also do not think it's simply hindsight thing.
Let's remember that one of allies was Joseph Stalin. Let's remember Soviets were trying to push some of their crimes on Nazis - like for instance Katyn massacre. And you have ignoring truth about many real attrocities on the other hand. Quite a mess.
Dresden know Nazis from comic books, and films when they are just sort of bland, death-cult spooks. Luccio knew people, and she had centuries of messy muggle politics remembered. And she also knew beings that would make Hitler, Stalin, Churchill and Eisenhower to shake hands, open fire from multiple machine guns and then be shredded into many bloody pieces (which arguably would make WW2 politics maybe a bit simpler). Beings like Dracul, Shagnasty, Outsiders, Denarians... She won't go all Manichean on mortals. Not even mortals with lot of blood on their hands. I mean remember what Jim wrote about soulgazing a Hitler.
(Or maybe she's just crypto-Mussolinian in heart
)
It is a bit of a cop out on Luccio's part because the WC was in a position to examine the stories of atrocities. Even though there were a lot of them, determining the truth of them all would have been possible for the council, though it certainly would have occupied a lot of time.
And then which attrocities would they stop? Hitler's? Stalin's? Japanese? Lot of places to be for organisation as small. Especially when you cannot just kill the bad guys. Especially if there are warlocks and sorcerers fighting on different sides that needs to be taken out - and necromantic death cult using World Wars for his own purposes.