Clearly, I agree with your conclusion, but I think your reaching on the doctor point. I assume you refer to Bashir’s being a genengineered freak, but I always had the impression that was an idea they cooked up midway through the series.
Also, black people are not genetically engineered.
As for Franklin, while the doctor was black, I don’t recall anything in the series which implied to me that role was written specifically to be a minority character. Perhaps the best man for the role just simply happened to be black. Or, they simply wanted a black actor somewhere and the man going for Franklin was the best candidate.