From what I did see of 24: Legacy I agree with you that the brother did have some layers. He cared for Nicole and bottom line, he cared for Eric as well. So that is a a step up from a random, sociopathic, blinged out 'banger. And for me it just goes to show you that he didn't even need to be a drug dealer at all for his character to work. As I said before, he could've been a businessman, politician, community activist, or even a cop, and still maintained that central conflict between the brothers. It's just that the white producers' in their limited imaginations can't see a successful black person without tagging them as an athlete, singer, or drug dealer all too often in entertainment. Other standard roles are domestics, preachers, and cops actually.
Now there are lawyers, doctors, and scientists, but in general, black characters in these roles are usually underdeveloped and have non-black spouses/significant others, if they have anyone or any life outside of the job at all. That is also an issue with black characters pretty much across all media. There is not enough exploration of their inner lives. They are only 'important' in relation to their connection to the white characters. And coming from white producers-it rankles-but I get that. To a white person who might not have much social contact outside the job-the job is where they will see these people and the writers rarely go beyond that to build up the characters. And often if they do, they go into stereotypical territory or the just as troublesome 'colorblind' characterization which makes black characters essentially white characters in darker skins. It's still an erasure of black humanity, albeit with a supposedly kindlier intention to avoid stereotypes.
And I think that is because the idea of blackness and black people is so warped and stunted in the imagination that some white writers automatically associate black with pathology and stereotypes and in their attempt to go beyond that, they just make the characters 'just like them' ignoring the vast swath of black people and black experiences that might be similar to their own actually but still different due to race. There's history, experience, and nuance they are completely oblivious to or ignoring outright.
So I do think its very important that black writers and creators continue to do their thing and get more spotlight to alleviate some of these problems. To be fair to 24, the earlier seasons presented the Palmers and they went against type for me. Granted they might have been more in the 'colorblind' casting kind of characters, but something read as distinctly black to me, and we got to see a delightfully scheming Sherry Palmer, the noble David Palmer, and also the other members of the family. After the earlier seasons black characters became more disposable. I particularly didn't like how Curtis was taken out and not really mourned.
As for the Untouchables, I would say the show remained popular because the non-Italian whites liked it and were fine with the depictions. I mean Southern Europeans weren't automatically accepted as white like white Anglo-Saxons when they first got here, so I can see some of those tensions still existing at the time of that show. Along with the Irish, I mean JFK had to mute concern about being a Catholic when he ran for president some fifty plus years ago. Few would bat an eye about a Catholic running today.