It’s certainly true that I know less about the air war in WW2 than the sea war, my father served in the Royal Navy and was on board the Prince of Wales when it was sunk, survived and spent the rest of the war in the Admiralty. I was born in WW2 and learned a lot from my Dad’s stories and the memorabilia he left me. So for specifics about the air war I rely on informed sources like this:-
en.wikipedia.org
It was the area bombing, particularly that of Dresden, that was so controversial. Not the targeting of the dams, which also impacted huge numbers. Hamburg isn’t a major population centre? I was there earlier this year. It’s pretty big.
Just as the bombing of Gaza by the Israelis is controversial today. For somewhat different reasons perhaps but still controversial because of the level of civilian casualties.