It's probably futile to argue this, but one man's exploitation is another man's empowerment. If you believe Tarantino's only reasons for making Inglourious Basterds and Django Unchained are to pad his bank account and glorify himself - which would require you to ignore the fact that he put his own salary on the line in order to get the latter made, among other things - then you'll be prone to believe that he's trivializing atrocity. If you understand that a fundamental motivation for exploitation cinema/cinema in general/art in general is to give voice to those who don't always have one in reality, you'll understand that while the film may be a humorous fantasy, it's not for lack of respect to the severity of history. The fantasy kills are presented as ultra-graphic and stylized and often hilarious, but the violence that mirrors actual slave practices is the opposite.
Personally, I wouldn't rank Django or Basterds higher than his top/first four (and I will always count Kill Bill as a single work, though I do find the second half slightly more glorious than the first). But if those two are #5 and 6, that's a quality fucking filmography.