in general election terms, swing voters in battleground states are the most important voters. the demographics of swing voters in those states can vary, but they are more likely to be middleclass whites.
where black women (and men) come into play heavily is in the democrat primary. so it may be arguable that blacks serve as kingmaker within the party, though it has to be said, the big money donors and party elite help determine which candidates are seen as viable. also, the states with the least black voters in them go first in the primaries, which is probably further shaping the choices black voters get to select from by the time the primaries move to the south.
black women are the most reliable democrat voters but black men are not far behind at all - certainly not enough to warrant the discourse that keeps happening every four years.