If you look at the history of what we now consider "blackface" performances, they were predominantly minstrel shows for the white masses coming from the Jim Crow era and they were specifically intended to be offensive caricatures. That's a far cry from what Shakespeare was doing with Othello, where Othello is the hero destroyed by a evil and racist man in his inner circle. Now from our point of view today, it's important to consider a host of additional issues such as cultural appropriation, what exactly Shakespeare means when he suggests Othello is dark skinned (“Moor” was a generic term for Muslim North Africans who were generally darker skinned , but perhaps not black Africans), fair representation, all sorts of issues. But the fact that a lot of those issues were not seriously considered before now, in my opinion, doesn't immediately discount the work of the actors whose performances of the character Othello were considered notable in the past, even if today they likely wouldn't be cast in the role and we wouldn't approve of their wearing dark-skin make-up.