Hitler and the Nazi regime were responsible for at least 20 million total deaths during WW2, in just under 6 to 10 years; including over 10~11 million in concentration camps (and 5–6 million jews). It's all well-documented and common knowledge.
That averages out at around 2~3 million deaths per year (WW2 over 10 million deaths annually), which is still far worse than anything Riliane ever did. As for Joseph Stalin, he had directly executed over 800,000 people in purges alone; with the Holodomor resulting in over 5 million deaths within just 2 to 3 years, and as many as 20+ million victims during Stalin's entire reign.
With that being said: She was still a selfish, horrible tyrant and is easily up there in terms of the worst dictators in history, but many world powers are objectively just as awful, if not much worse in the long term. Of course, she still had the potential to become worse; but nowhere near as evil as actual monsters and fictional villains like AM, Frieza and Palpatine.
Just wanted to correct you on that~