You know what else causes the movie to lose its historical integrity? The actors speaking English. There will be a million anachronisms in the movie and million fictional aspects in it too. All movies reflect some modern sensibilities whether we want to believe it or not. So if this black actress does a good job portraying Helen, so be it. If she does a bad job, then Nolan made a bad choice.
“ There will be a million anachronisms in the movie…”
The best anachronism is the deliberate one from Monty Python “Holy Grail”
Where they constructed the wooden Trojan horse using chainsaws.
To expound on a point I made in an earlier post, I don’t automatically have a negative reaction to “race swapping” of historically white roles. There have been plenty of cases where a minority actor has been placed in a historically white role purely for political / ideological reasons and that is wrong and usually turns out to be a disaster. But I also accept that a director may have a vision for a role that involves a certain actor or actress who is not white and I accept that the director should be allowed to have the freedom to cast who he or she wants. That is part of artistic freedom. There are many non-white actors who are excellent - for instance, I’d watch Denzel Washington in pretty much any role.