Sure, if you want to go back to the Jim Crow era then it's pretty easy to say that blacks were denied a lot of opportunities. If you want to go for the length of Will Smith's star movie career (Bad Boys 1995), that's a little more topical and reasonable. You can also see from those dates in the OP that it's been getting a LOT better. Over the last 80 blacks were vastly under represented. Over the last 30, mostly short changed. Over the last 20, very fair. Over the last 15 years (Since Denzel Washington and Halle Berry both swept the Best Actor/Actress) it's 9/60 = 15% which is actually slightly over represented.

Statistically there should be a black winner in one of these four categories every other year or so. I don't think there's any racism in there not being a great black performance this year. Is there racism at the basic foundational level of recruiting new black people into the movie business and developing acting talent? Probably, but that's a different issue. The Academy Award voters have shown time and again they will reward good black actors/actresses. It's just a quirk that 7 of the major films this awards season are based on real life events and those stories have very few black people in them - Jobs, Bridge of Spies, Big Short, Spotlight, Trumbo, Danish Girl, and Revenant. Those movies ate up 11 of the 20 acting nominations alone - and virtually all the male ones excepting only the franchise character of Rocky in Creed and the based on a book Martian. Biopics of white people were the rage this year.

Since Will Smith is one of the figureheads of this protest, it's also worth noting he was nominated for 2 acting Oscars. Both times he lost - to other black actors.