You can't refer to the underlying factors behind the lesser success of Black Females as blatant racism, but conversely it would be pretty avoidant to assume that at least ignorance, to some degree, doesn't play a role in how the audience responds to different acts. The majority of TV viewers are older and hold more conservative values, both of which majorly clash with the aspects of a Black Female act. Both sides have foundations that make them horribly incompatible. It's only worse when the average viewer isn't searching for the vocal prowess of a church-grown vocalist. That is just a result of environment but if there's anything you can put in a negative light its when you see comments verbalizing that incompatibility, aka the mass of Facebook comments of people giving out the most minute criticisms they can whip up. And there is no doubt that if you don't really align with the main demo's preferences then you'll get a lot of crap.
And even if a Black Woman does well on TV (I don't think AI needs to be a part of the discussion), it is no doubt only when a lot of things are in her favor, from being on the right team, being a promo favorite, or just having little real competition.
Tessanne Chin and Black Men that made it far onto this show shouldn't be a part of the discussion of race matters either, seeing as how Tessanne goes under the radar as someone who does not LOOK Black, and the latter have a better position in the social hierarchy than Black Women do.